Art Shift: Starting with the adaptation of The Empire Strikes Back, the art changes from Carmine Infantino's loose, angular style to a more detailed look with much closer likenesses to the film characters (usually veteran inker Tom Palmer over Al Williamson or Walt Simonson.) The last issue also has a strikingly different style than its predecessors.
Audio Adaptation: "Droid World" and "Planet of the Hoojibs" were both adapted as book-and-tape sets.
Badass: Luke once duels Orman Tagge, who'd been training with a lightsaber for almost as long as Luke's been alive, ever since Vader forced him to get cybernetic eyes. Luke had only ever dueled with remotes, but he called on the Force and over matched the other. Tagge pulled a trick... it didn't work. Later, Tagge was in shock.
"…h-he didn't kill me…! Didn't…need…to…! Controlled stroke so perfectly…destroyed my cyber-vision…without harming me…! He…was that good…! Th-that…good…!"
Badass Boast: Done in order to activate a droid's capture programming, but still.
"Yoda said it, Artoo: There is no try! Only do.. or do not! And I mean to do! This can't stop me! Nothing's going to stop me! I'm Luke Skywalker... destroyer of the Death Star! I'm the one who dueled Darth Vader and lived to tell about it!"
Breakout Character: Lumiya is the most famous character in the series and the only one to feature in an important role in later Expanded Universe stories but she had a mere six appearances (plus seven more as Shira Brie). Her lightwhip appeared in just three issues but is similarly iconic.
On the heroic side Dani became this, she had a major character arc, effectively became a Sixth Ranger to the heroes and appeared in more issues than any other Marvel created character (17 plus various mentions elsewhere). Unlike Lumiya she hasn't been seen or referenced much since the comics run ended but as the prototypical Zeltron she's had a lot of influence (Delilah Blue from the Legacy comics is clearly her Expy.)
Canon Discontinuity: A lot of the stories are considered non-canon at best, simply due to being supplanted by later material. One example is a flashback story where Luke's father, Darth Vader, and Obi-Wan Kenobi (three separate people) save a planet together - although that story was written before The Empire Strikes Back, and therefore a professional example of being Jossed. Mind you, one of Lucasfilm's resident kings of Continuity found a way to make it work...
Another good example would be Jaxxon, a giant green bunny man. Legend has it that Lucas stated that Marvel were to never, ever, use him again. His race, the Lepi, has resurfaced in more recent RPG material.
As can be seen here, Marvel Star Wars is considered to be on a lower level of canon than most of the Star Wars Expanded Universe, although its material can be used or discarded as other authors wish, as long as it does not contradict the higher levels of canon.
An issue of the Marvel series deals with Wes Janson's death. Wes is alive and well in the X-Wing Series, set a few years later. Supplemental material, specifically Adumar: Pilots Wanted, Retcons this rather than ignoring it completely. It's a story Wedge would tell new recruits before calling in Wes. Even Luke fell for it.
But the original example has to be the TIE Bomber.
Zeltrons, too, the species of hedonistic red near-humans. The Zeltron attraction to Force-Sensitives is actually a plot point in Coruscant Nights.
Chekhov's Boomerang/Brick Joke: Drebble. Lando owes him money because Drebble claims Lando cheats at cards. So Lando uses him as a fake identity. Lando's work is so good that the Rebels want to give Drebble a medal!
The Chessmaster: Darth Vader. The Marvel series really ran with the idea of Vader being an evil genius to a much larger extent than anywhere else in the Expanded Universe. Largely by necessity, as Lucasfilm generally forbade direct confrontations between Vader and the main characters, as they might have upstaged what they were planning for the movies.
Shown literally in the cover for issue 35, "Dark Lord's Gambit".
Dark Elves In Space: The Nagai have many typical Elf traits - they are tall, slender yet strong, agile, androgynusly good looking, are arrogant towards most other species, have angular features and even pointed ears.
Does This Remind You of Anything? / Anvilicious: The entire Mary storyline. Luke goes on a mission to help guerrillas fight the Empire. While there, he falls in love with a guerrilla named Mary. They succeed, but then they turn on each other, and in the process, Mary is killed. Yes, this was around the same time as Iran-Contra. Why do you ask?
Dream Tropes: Luke's Force-tinged dreams come up three times in the series. The first, "The Empire Strikes", has him go into a coma after sensing Vader's mind for the first time, and having to fight a Vader-shaped manifestation of his fear. The second time is when he's infected with the Crimson Forever plague, and fights a Vader-shaped manifestation of the sickness until he gets a burst of insight from Obi-Wan and Yoda and lets it strike him down. The third time, he... sees a Vader-shaped manifestation several nights in a row, talks to it with the spirits of his teachers and father, and discovers that it's a new Sith Lord. Only then can he see it as something not-so-Vader-shaped.
Enemy Mine: Leia and Luke are forced to combine forces with a squad of Imperial commandos to survive a hostile planet in a 1980 storyline. While one of the commandos is a complete scumbag their overall leader is portrayed as a sympathetic Worthy Opponent who just happens to be on the wrong side and Leia even tries to persuade him to defect. He refuses, using a My Country, Right or Wrong arguement.
Equal-Opportunity Evil: The Marvel series probably has more female antagonists than the rest of the Star Wars Expanded Universecombined. Lumiya is by far the most famous but there are many others ranging from serious villainesses like Kharys to one issue annoyances like Captain Traal. There are even a couple of nameless female Mooks!
Eye Scream: Comes up in Orman Tagge's backstory. Vader blinded him, forcing him to resort to a cybernetic visor. When Luke fights him, he cuts off Tagge's visor◊ without hurting him, leaving him (temporarily) blind again and BSOD-ing.
Faith Heel Turn: After he shoots down Shira, Luke has a crisis of faith in the Force
On a more general level anti-droid prejudice is depicted as very common, which retroactively fits in very well with what we later see of the Clone Wars.
The issues featuring bounty hunter Valance prominently feature anti-droid prejudice, but take it to a new level. Valance, who obsessively hates droids, is a cyborg, and it turns out they're subject to prejudice, as well.
Getting Crap Past the Radar: Zeltrons. Given that Marvel (and Lucasfilm) had a very strict "No gays" policy, the Zeltrons could be this trope personified.
In one issue, Luke is surrounded by Zeltrons, and he's keeping someone from poisoning an Imperial governor because even chaotic has standards. Somehow, Leia ends up posing as a singer. See the case of the Lahsbees to understand why one immature Lahsbee became a huhk while listening to Leia. Then Luke is surrounded by Zeltron fangirls...and one fanboy, all too fascinated by the song to make moves on him like they have for the whole of the issue. A worried Luke hopes she knows a lot of verses.
Heroic Build: This was very much a Marvel Comic, and the art often followed this aspect of Marvel's house style. Particularly obvious in the "corner art" depiction of Luke on the cover of every issue. With a bit of art touch-up, the "swordsman" would be indistinguishable from Marvel's Conan the Barbarian.
Depending on the Artist. In The Crimson Forever, halfway through the series, he looked like this◊. Near the end he was usually drawn as muscular but slim, as in My Hiromi◊ - however, in the last issue, All Together Now, he looked like this◊.
Idiot Ball: Luke and Dani think Kiro's dead because he fell in the water fighting an enemy, the water got bloody, and he never came up, and he's a fish man!
They aren't really sure it's him, but when they get back to their ship and see that Shira/Lumiya has been released, and the flower Den gave to Dani there, it pretty much seals the deal that Kiro lost (although it turns out later that he survived and made it back to his home planet).
Jedi Mind Trick: Played for Black Comedy in one issue with Darth Vader using a Mind Trick to persuade an incompetent officer to go for "some fresh air", by stepping out an airlock. Another issue gives us a rare glimpse of the aftermath of a Mind Trick when Luke uses a long distance one to make an Imperial station commander to drop her shields. The commander mindlessly orders the shields dropped then comes out of her trance and is surprised and angry to notice the lack of shields, blaming it on her underlings' incompetence.
Mistaken Identity: In "Chanteuse of the Stars", said chanteuse is something of a diva and quits before a show. Leia, trying to evade recognition, puts on the woman's wig and is mistaken for her by the chanteuse's own manager.
Never Say "Die": Generally averted, but just like in the films, there are some odd examples where "destroyed" is used instead. And in the Crimson Forever arc, Luke is killed by the eponymous disease (he gets better) and Leia and Lando have to continue on without him - but they never say die. Just that he succumbed to it. And since everyone else who'd contracted it had died...
Also in the last issue of this arc Leia is contacted with an offer for a way to stop the plague and undo the worst of it - including the death of Luke Skywalker.
New Powers as the Plot Demands: Luke gets these on occasion. The comic directly after ESB has him slowing his heart rate and breathing to the point where a droid monitoring his life signs thinks he's comatose, though he's up and moving. In another comic, he uses the Force to find six bombs and make their primers explode, but not the bombs themselves. And of course, there's the long-range Mind Trick mentioned above.
Out of Focus: The Empire itself in the first year or so of the series run. Between issue #6 (the last installment of the adaptation of A New Hope) and issue #18 the Empire did not appear 'onscreen' at all except in the form of flashbacks which the villains in the interim being space pirates, mercenaries and raiders. After this though the Empire was almost never Out of Focus again until the post-RotJ stories.
Overtook the Manga/Overtook the Series: The comic got ahead of the movies themselves after the first six issues (which were adaptations of the film). Ironic since it's a comic book adaptation of a screen franchise.
Remember the New Guy: Sort of. Wedge Antilles was in A New Hope, but never featured in the non-movie-adaptation comics until "Hoth Stuff", when he was suddenly Luke's oldest friend and had Biggs Darklighter's backstory.
The Reveal: The new Sith is... Luke's crazy ex-girlfriend!
Reverse Polarity: In #52: To Take The Tarkin, Leia switches a couple of wires to reverse the polarity modes of The Tarkin's fire controls. When the station tries to fire its superlaser on the Millennium Falcon, the superweapon explodes.
Running Gag: The number of times either Luke or Leia attempt a Relationship Upgrade but are interrupted by something - usually the main plot kicking off - approaches this. Which becomes even funnier after Return Of The Jedi revealed that they're siblings.
Luke actually looks like Rambo in the last issue, with his hair growing literally five inches for one issue, and he's very buff, constantly shirtless, and holding a giant laser cannon. Yes, that is as bizarre as it sounds.
When he's infected with the Crimson Forever, a rather dramatically named plague, he has fever dreams in which he fights Vader while shirtless. Despite wearing a shirt while lying in the quarantine wing.
Then again, he was dying. It's amazing we got something as lucid as fighting Vader while shirtless instead of an hour or two of Luke following unicorns through an acid trip.
Title Drop: The 89th comic is called "I'll See You In The Throne Room!", which on the first page is shouted by one of the characters.
Too Dumb to Live: After being blinded by Darth Vader, Orman Tagge became obsessed with defeating him, procuring a lightsaber and training endlessly with it. He also had a dirty trick in mind that he planned to use if it came to that, which he was forced◊ to use on Luke◊ - namely, he planned to have the lights go out during the fight. With his cybernetic replacement eyes, he'd be able to see in the dark. The poor man never understood the power of The Force...
Unwanted Harem: Luke around Zeltrons, at least until he apparently gets used to them. "Chanteuse of the Stars" has him actively fleeing from hot red women who think he's the most beautiful man they've ever seen. Eventually one of them (Dani) becomes a close, platonic friend partly because she fell for someone else and so stopped chasing him and partly because she went through a lot of Character Development.
Villain Episode: "The Hunter" is a combination of this and A Day in the Limelight as the focus is on both the evil cyborg Captain Valance and the surviving heroes of the group Han and Chewie assembled in "Eight for Aduba-3" from earlier in the series run. Uniquely none of the core heroes (Luke, Leia, Han, Chewie and the droids) appear outside of flasbacks.
Villains Never Lie: After Luke apparently kills Shira, who was popular with Alliance personnel, he goes on sabbatical to grapple with his faith in the Force, soon finding that Shira had been lying about her homeworld and tragic backstory. Vader communicates with him and tells him that not only had she been lying, she'd been working for him the entire time. Now the Alliance is against Luke, and the only way he can keep from being a pariah is to join Vader. Luke is shaken by this, but actually goes to try to find Imperial records on Shira before he outright believes his father.
He also needed the records in order to prove his innocence.
Villainous Valor: Baron Tagge in his lightsaber-duel with Luke. As an expert swordsman, he believed he could defeat a Jedi. He doesn't, but for a while he makes a credible showing.