Flexibility is king. Those encounters for this session that the player characters have somehow managed to be thousands of miles from? You'll get a chance to use them someplace else. Improvise (or better yet, have some backup encounters planned), and roll with it.
Highly Visible Ninja EDIT: Also, interesting characters are indeed vital. Just don't be surprised if the players decide that one of them is annoying and attempts to murder the guy you had planned to give out the next three plot hooks >.O
edited 17th Apr '12 8:43:17 PM by TeChameleon
Don't bother with making super detailed character sheets for major NP Cs, unless they're jointing as a party member. Just stick to the basics (combat-related, special powers-related, basic appearance, special goodies, etc.) You are probably not going to need to know that the head of the mage's guild has high skills in crocheting and leadership. Just improvise those stats and facts as you need them.
Make all of your battles 50% harder than you think they can handle. It still won't be enough.
Fight. Struggle. Endure. Suffer. LIVE.Player characters are hateful monsters who will bring destruction and misery to everything you and your NP Cs hold dear. Plan accordingly.
Politics is the skilled use of blunt objects.Always make sure to put player enjoyment as priority number one. Players will forgive any and all other mistakes you make (plot holes, rules flubs, etc) as long as they have a good time every session.
If I were to write some of the strange things that come under my eyes they would not be believed. ~Cora M. Strayer~There is nothing wrong with banning something before the game begins. This includes a particular chunk of rules that you are having trouble grappling with, inappropriate character concepts, and even particular players.
I'm bad, and that's good. I will never be good, and that's not bad. There's no one I'd rather be than me.Once again:
ROLL WITH IT.
Whatever happens, you can either make something up from scratch or at least improvise a transition to something you did prepare beforehand.
Also, if your players desperately try to go Off the Rails in the same direction, you're apparently railroading them too hard. And you forgot something obvious.
Every boring combat can get a little more interesting with right terrain features. Lure players into traps or make them lure critters and/or mindless cannon fodder into traps. Put up some interesting scenery. And have the appropriate rules handy, just in case someone wants to smack a goblin with a shield to knock him off a bridge. Or something.
"what the complete, unabridged, 4k ultra HD fuck with bonus features" - Mark Von LewisAlways assume that your players will manage to a. kill b. seduce or c. befriend anything or anyone they interact with, and plan accordingly.
This includes both the terrain and the setting.
No exceptions.
edited 27th Apr '12 12:54:38 AM by Korochun
When you remember that we are all mad, all questions disappear and life stands explained.Don't bother thinking too hard about what you're going to name locations; your players won't remember them anyway. Just steal them from fantasy novels, mythology, or Canadian geography; all your players are functionally illiterate, and won't recognize them. (Seriously, I've done the last one, and no one caught it. They were all like "Etobicoke? Did you spill a bag of Scrabble tiles?")
Another TL:DR post.

Interesting characters aren't all you need, just 90% of it.
Proud Knight of the Lambda Calculus.