So, we've talked about a number of different things for running various kinds of games, but for today I want to take a look at the actual session itself. Now, before going into this, I need to make it clear that I generally run "guy" games. By this I mean that action is a serious, and major, part of my games. While role playing, exploration, mystery, and adventure can all be big parts of it as well, combat is generally a fairly constant thing to be seeing. As such, most of this advice will be geared towards what I do for my games, though hopefully you'll find it helpful as well.
The Average Session
Now, despite what some people will tell you I find having an 'average' session plan to be handy. Why? Because games are done episodically in a lot of ways, you meet your players about once every week or two and in those sessions you continue the story. Because of this, I've found that games work better when you treat it more like an episode of a weekly show or an issue of a comic book more than a chapter of a book. Why? Because chapters generally don't have a specific beginning, middle, and end when it comes to story telling and giving your game some semblance of these can make inidividual sessions more interesting. I'm not saying I always succeed at this, but on average I try.
In the beginning of the session you want to deal with the stuff from the end of the previous session. If this is the beginning of a new story, then you just go into setting things up for the story. If you are in a story already though, and you ended last session properly, there should be some things that need resolving or going into before things can really get moving. Give some clues to the story, get some stuff done, and move things along. I can't really tell you how to do this, because really every session is different, just in general remember you are picking up from where last session ended and using this time to continue that into this game.
The Middle, a.k.a. Combat
Generally speaking I try to keep it to 1 combat a session. This is for a number of reasons, one, generally you can count on one coming up, two in a game where players made combat capable characters they want to fight, and three it gives the session conflict and a chance for drama and failure really quickly. Going into the session I like to know what the combat will probably be, but if I don't know I'll look for a way to slip one in. Sometimes this isn't appropriate, but in a game where one of the main elements is action you generally can. This is also the middle as much as possible because combat is the most mechanically intensive parts of most sessions, so lets give it a spot where it has time to go a bit long without risking you running your game until 2 or 3 in the morning when it normally ends at 11.
The end deals with the resolution of the combat, generally people are injured from the fighting, the fight itself may have left clues for things. Wrap up the fight, get things moving on the plot again that the fight may have shook up or tried to delay. You want the end of the session to have the feeling of an ending, but you also want to (unless you just wrapped up the current plot line) leave a hook for the next session. A reason to get the players to come back to things. Yes, they just fought their way up the tower and found the mage, but the mage has an ace up his sleeve. Sure they just stopped the bank robbers, but why did one of the crooks have Bob's character's girlfriend's picture on him? Something, some reason to make them look forward to coming to the next session.
It really is as simple as that, that is my average session. We begin things, pick up on old strings of thought and plot and move on into it. This movement brings about the combat for the session, which resolves and leaves us in the end game where any smaller threads introduced for the session are resolved, a suitable end point is found, and hooks are left for the next session. Simple really, but a good thing to be planning for with your session.
The All Combat Session
This kind of session happens on occasion. After all we're doing a more action type game, and even shows based less on action (like Star Trek) have episodes dedicated to the heavy combat. If you look through a lot of combat shows you end up with a format like SA-SA-SA-SA-BIG FIGHT-SA-SA-SA-SA-BIG FIGHT and so on, where SA stands for "smaller action". It's also likely to happen in your game where some sessions are just going to be dominated by combat. Don't be afraid of it, but don't get lazy with it either. Combat can take a long time, and can be VERY boring to sit through, even if you are participating. An all combat session though needs to be exciting. So how do you do that?
For one, you need to relax on the rules a bit in an all combat session. Do what you can to stream line the process. If it's an army vs. army fight, or there are a lot of enemy soldiers reduce their normal wounds down to four statuses. "Unwounded, Wounded, Crippled, Down". It makes it easier to keep track of things, and lets you stream line things. One guy takes two hits, neither of which are particularly damaging? Well he's still crippled because he got hit twice. One hit is particularly powerful, but just shy of a one shot kill or out? Give the player the benefit and move the person to down. If they're important, than just put them in crippled. The point though is to make things easier, for yourself and the players. You also want to be a bit more forgiving with what players want to do in a round, let them have some fun, try to keep things moving instead of bogged down with rolls. I mean, they're going to be rolling dice like crazy anyhow. Why not keep it to the important stuff?
Another thing you may want to consider in an all session combat is increasing the round timer to like a minute, and using that as a way to relax people's restrictions. Their attack rolls and damage rolls aren't an individual attack but how effective they are offensively over the course of a minute. Attacks on them aren't inidvidual hits, but nicks and cuts sustained over that minute. It can really help make things go faster, and when you end the fight with "so after ten minutes of frantic combat" as opposed to "so a minute later" everyone will feel a bit better.
The last thing you want to remember is to describe things. If your players aren't describing their actions, do it for them. Give them a visual picture of what is going on, play up their hits, make them bone shattering. In game what is going on is violent and exciting, at the table it's dice rolls and numbers. Show them what is going on, help them picture it and they'll come right back to you with some of their own stuff. It will also help the session be fun and exciting as opposed to slow and boring.
The No Combat Session
Some of the most fun I've ever had as both a GM and a player has been in the sessions where the dice were never picked up. Role playing carried the session, and at times the GM wasn't even needed for a large part of the game. That being said, for some people these sessions can be boring and you need to be aware of that. Not rolling dice doesn't mean excitement can't happen. You just stream line things a bit more, assume stat/skill scores can be effective to that level and go. However, if all your players are smiling and talking and laughing it up in character then why not let them go at it? Keep up with it, maybe interject with an NPC. If time is of the essence, by all means let them know they're wasting time, but don't stop them. The point of the game is to have fun after all.
No combat sessions are best to have shortly after all combat sessions, or shortly before. Either the preparation and tension building leading into the big fight. Or the tension bleed off and the 'we did it!' for after the big fight. Use them to set things up, get other things rolling. Dealing with the consequences of actions that aren't mechanical (or aren't directly/specifically mechanical).
I guess what I'm trying to say with this is that, if nothing else you should plan for your sessions basic structure. Be maleable to change within it, but be prepared. Having a "general session plan" that could be applied to 95% of your sessions is a great idea, but also be prepared for sessions that shake that up a little bit from time to time and keep people guessing. The second a player goes "and time for this sessions big fight to happen" like they were absolutely sure it would happen might be a time to hit them with a few non-combat sessions (at least don't start combats on your end). However, even with that, the most basic level of game prep is your session structure. From there the rest of the plan can come into focus, and when you are specifically planning for the Beginning, Middle, and End of each session your games will gain a more distinct narrative type feel to them, and when you do it right your players will be excited to see what happens next and really really want the next session to be here already.
Either way though, have fun with it.