Aliens in fiction are always foils of humanity, given that we're the only sapient species we have for comparison. So when you're designing aliens, the question is, what are you trying to say about humans with them?
It sounds like you're going for a Not So Different theme, so I'd suggest making them... well, not so different from humans. Four limbs, a head, and a torso in roughly familiar places, probably mammals, etc. Make sure the differences you give them will be obvious without an Infodump, though — maybe they're covered in fur, or have armored skin, or have a tail. Maybe their primary sense is smell or sound instead of sight. Maybe they have some sort of physiological quirk where they feel anger and fear as the same emotion, so when in battle there's no difference between Unstoppable Rage and Heroic BSoD. The point is to make them recognizably and obviously different on the surface, but ultimately, fundamentally the same as us.
Really from Jupiter, but not an alien.Excellent ideas Jovian, thank you. Yeah, you're right - Not So Different is what I'm going for, which I'm hoping will lead to some considerable irony in the final chapter.
With cannon shot and gun blast smash the alien. With laser beam and searing plasma scatter the alien to the stars.Have a race of aliens Put On The Reich and race in a WH 40 K esque craft, then?

In the short story that I am currently knocking up, there will be a chapter from an alien point of view. The twist is that this is during a period of that species' history that is roughly analogous to the Second World War, and the alien whose point of view we're seeing is right in the thick of it.
I'm currently scratching my head a bit about this. What interesting twists can we put on a world war being fought by a species that has evolved quite differently to us? What the species looks like, how it evolved and how its history developed are all very much up in the air right now.
The short story, by the way, consists of three chapters, of which this is the second. The first is from the point of view of a German soldier fighting in the Battle of the Bulge, and the third is set far in both species' futures when they fight a First Contact War.
I'd be grateful for any ideas.
With cannon shot and gun blast smash the alien. With laser beam and searing plasma scatter the alien to the stars.