It amuses me to no end that this post is going up late, because it is talking about being prepared. Now, when I say preparation I do mean for the next session of the game you are running, but it can also be much further along then that. Why? Because when you're properly prepared for a game, you'd be amazed at just how long you can go before you need to sit down and think it all out again.
The Most Important Thing
The most important thing to remember when doing prep for a game is that you're not going to be prepared for everything. Your players are very likely clever people, and if not they're very likely impulsive people that are playing in a universe with no real-world consequences. This means that, on occasion, they will do the completely unexpected. However, being prepared for other things - and knowing your players - can make those moments less awkward. Hell, sometimes it will make them the most awesome moments of an entire campaign.
Still, the lesson to take here is that there will be holes in your plan. Your players will occasionally go off into unchartered territory. If the players don't, the dice will conspire against you. It's going to happen, so just relax and be prepared for when it happens.
The next most important thing is to have your priorities straight. Priorities will let you focus on the most important things, and leave the less important things for later. This will be different for every GM, but knowing your own strengths and weaknesses - or even just your perceived strengths and weaknesses - will make a huge difference here. The rest of this post will be talking about this, and some things to consider.
The "What Happens"
For me, this is the most important part of game prep. Stat blocks and city maps aren't super important, they're just fun to have and can be helpful. Your players will forgive you for not knowing an NPC name. They'll be ok if they have to wait a bit to find out just what that magic sword does. However, they'll notice right away if you don't know what happens next. Yes, sometimes this will happen no matter what, but it is still the most important thing - again, to me - to know going into a game.
When working on this, start with considering the PCs actions. That should be your top priority when figuring out what comes next, as it keeps the action nice and focused on the PCs themselves. Next, consider what the PCs want. Then consider what the NPCs want (starting with the PCs opposition) and determine how these things are going to clash and make what happens.
When it comes to NPCs I've found that motive is the most important thing. Understanding what an NPC wants, and how badly, will make them a lot more believable, consistent, and fun to play against then a particularly nasty stat block or cunning bit of voice work. Do those help? Sure they do, but it is our wants that define us as people. Our wants make us human. So, start there and don't worry if you can't get anything else.
What I am trying to say with this is that, if you have time for nothing else when doing game prep, take some time to think on what is going to happen, and the motives of the people that are making those things happen. Everything else can be improvised if necessary, or generated on the fly if you need it right now. Motive and the "what" of a session though will keep things moving along.
After all, your PCs aren't going to know the difference between *dice roll, pretends to think* She successfully stabs you with the poisoned knife and *dice roll, checks premade character sheet* She hits you with the poisoned knife. They are going to notice that pause when you have to think if they ask "Why did she do that?!"
More To Come
I'm going to talk a bit more about game prep in some of the next few articles. Tomorrow has a special holiday theme to it though, and is part of a project being put on by nevermet press. Yeah, yeah, clicking that link may spoil the surprise, but if you're an avid blog reader, you probably know about it anyhow.