1: Use Notes - Index Cards, a Tablet, or Computer
There are a lot of rules for any roleplaying game, and flipping through books is the number one reason sessions grind to a halt. Use notes and index cards, to track monster and NPC stats, relevant rules and mechanics, and any other important information. I personally use a laptop for all my GMing. Not only can I quickly look through my notes, but I can very easily search online rules databases for the grappling rules.
Bonus Points: Get a responsible player with a tablet or smart phone to be on rules duty, ready to look up anything.
2: Divide GM Duties
As a GM, you are the bottle neck. While the players simply need to keep track of their own characters, you need to keep track of all NPCs, enemies, plot, weather, and cycles of the moon. To make your life easier, distribute some of your duties to your players, especially during combat. After writing initiative on an easy to see location, have another responsible player track and manage it. Make it the responsibility of the victim or instigator to track per round effects such as Sleep, Hideous Laughter, or rising water. If a rules determination is needed, assign it to another player and move the session forward (if possible) while waiting for an answer.
Bonus Points: After initiative is rolled, have the players switch seating order to reflect initiative.
3: Roll To-Hit and Damage together
This is a classic, and often under appreciated rule: Roll your to-hit and damage at the same time. Most people will first roll you save the five seconds or so it takes to pick up and roll your damage dice. Lets say Barbar the Barbarian is attacking at +10 for 2d6+8 damage. Barbar would roll a d20 and 2d6 all at once, only calculating his damage if the d20 was a hit.
Bonus Points: Have separate little piles of dice on the table for each of your attacks, ready to be rolled at a moment's notice. For example, a rogue might have two piles - one for attacks with sneak attack and one without.
4: Prepare 3 Random Encounters and 10 Random NPCs
Note: Drawn directly from the 10 Tips for New GMs, which has a few other time saving tips
Have a list of random encounters and NPCs ready before the game. These do not need to be fully developed - they are just something to quickly draw on when put on the spot. Sketch up two or three encounters that your players are likely to stumble into, be it a fight with a gang, an assassin come to kill a PC, or a random fight with an owlbear in the woods. Get the statblocks of each of these enemies and a general gimmick for the battleground (on rooftops, plenty of trees, overlooking a cliff...). This way you will be able to quickly and seamlessly move the game forward.
Similarly, generate a list of about 10 NPC names and choose one distinguishing feature about each (missing left hand, persistent cough, drunk). Next time you are put on the spot for a random NPC, you have something to pull from. The heroes want to go to a shop? The shopkeep is the first NPC on the list. The guards come to arrest the PCs? The captain is the next NPC. By having a simple list of names and attributes, you can make your players believe that they are in a real world inhabited by real people. If you respond quickly enough, you can even make them think you have planned for every contingency!
Bonus points: Prepare one shop, one tavern, and one guard in detail, as your heroes are likely to encounter one of these each session.
5: Use advancement track, drop XP.
I have never been a fan of XP. It decreases roleplaying, rewards grinding, and takes away from immersion. And now, there is another reason to hate it! Using XP slows down gameplay, both during distribution and calculation. If you are using an adventure path, simply follow the advancement track and advance your players as the adventure path suggests. If you are playing a home-brew, advance the party every couple sessions as you see fit.
Bonus Points: If you absolutely need to use XP, distribute all XP at the end of or between sessions.
6: Don't use a GMPC
Unless it is crucial to the plot, don't use an NPC in the PC's party. The party may not have a healer, a tank, or any ability to detect traps - that's fine, its part of what makes the party what it is. Don't get rid of that by rounding out the party. A GMPC just takes away from the "screen time" of the PC's, and is one more thing for you to track as a GM. It will slow down gameplay without adding anything to it.
Bonus Points: When an NPC is traveling with the party, make sure that he is either useless in combat or incapacitated and unable to contribute.
There are a host of "administrative" tasks that should be taken care of in-between sessions. Never level up mid-session, as that will bring game-play to a screeching halt. Even worse, the quicker players will be left with nothing to do while the slower players work. Instead, have players level up between sessions. Additionally, unless you value the role-playing aspect of it, have players purchase items between sessions.
If a player comes to a session without having leveled up or purchased items, start the session anyway. He plays with what he has, and next time he'll be ready.
Bonus Points: Encourage role-play between sessions through e-mail, internet forums, or a wiki.
8: Ensure Players Know their Combat Actions Ahead of Time
Hesitation during combat is perhaps the number one killer of game time. Players should be experts on their characters without having to look anything up. Make sure that they are thinking about their actions ahead of time, and are aware of their turn in the initiative order.
How to encourage this? First, make sure that they have all of the information they need to play. If they have power attack, make sure they have their attacks calculated with and without the feat. If they summon monsters, make sure they have the stat blocks in front of them.
Second, and most important, delay them if they are not ready on their turn. It may seem harsh at first, but it will do wonders for your game. If a player does not immediately declare his actions at the start of his turn, say "I'm going to delay you unless you say what you are doing." Give him another 20 seconds or so, then move him out the the initiative order and let the next person know it is his turn. The slow player re-enters the initiative order when he declares his actions.
Bonus Points: As the GM, make sure you are ready for your turn too! Before the session, read every enemy's stat block and determine some basic strategies. Fall back on those if you have to think for more than 10 seconds on your turn.
9: Keep Side Conversations to a Minimum
You are going to have to decide early on what kind of game you want to run. Are you okay with side conversations and a more social feel, or do you want to make sure game time is game time? If you want to stop side conversations, the best way to do that is to directly engage the distracted players and move the session forward. If Jack and Jill are discussing the results of the Super Bowl, have the king address their characters directly: "You still have not answered my question. Are you ready to embark on this epic quest?" Players get distracted because they are not interested, and the best way to keep them interested is to directly engage them. Keep the session focused, and your players will learn to stay focused.
Bonus Points: If you are doing longer sessions, you may want to add in a break or two. Judge your players and act accordingly.
10: Start on Time
The last rule is fairly simple. If your sessions start at 6pm, then the action begins at 6pm. Don't wait for late players, they will simply miss out. After a few sessions, players will learn to arrive on time.
Bonus Points: If you don't want to be such a stickler, order food, chat and perform any other non-game duties at the start of sessions. That way you can be ready to go by the time everybody arrives.