- Know your limitations.
The most important thing to do in any billiard game is to know what you can and cannot do. You should know what shots you can make with a high percentage (4 out of 5 or 80%) chance of success.
- Reduce unintended consequences.
The most common way a player gets in trouble is by the unintended consequences from the cue ball wreaking havoc after striking the object ball. Having a good idea of what's about to happen after your cue contacts the cue ball is the key to getting another good shot.
- Never put more energy into a shot than is necessary.
A player who can make a shot but shoots too hard will fall victim to the unintended consequences rule. The more energy that's put into a shot, the harder it is to know what's going to happen. Reducing the variables in the shot by reducing the energy is the easiest way to improve your game.
- Only shoot high percentage shots.
If you're left with nothing but low percentage shots (low percentage: make that shot less than 4 out of 5 times) then instead of taking that shot, shoot a leave. It's far better to leave your opponent in a tough spot than miss a low percentage shot and fall afoul of the unintended consequences rule. There is no shame in shooting a leave. Using this methodology will allow you to beat much better players more often.
- Save key balls until you can run out.
A key ball is one that is blocking one of your opponent's balls, securing a hole or blocking the 8 ball. Having one key ball can win you a game. Shooting it early can result in a loss. Your opponent will probably work hard at removing that key ball so let him waste shots doing it. Only shoot your key balls when you're ready to win.
- Break up problems early.
It's far better to solve a problem while the game is young. You can't run out until you've fixed all your problems so get to them before they become make or break issues. If you're playing a better player, and you have a ball tied up with one of your opponent's, you can let him solve the problem for you. Put him in a position where he has little choice but to break out your ball for you.
- Control the table.
Get your opponent to shoot the shot you want him to make, not the one he wants. For instance, if you leave him nothing but one of his key balls to shoot at, he may have little choice but to remove that obstacle for you.
- Play at least two balls ahead.
The further out you can think, the better chance you have of running out. Don't depend on dumb luck to give you your next shot. Thinking carefully about your order of battle will allow you to run out sooner. If you don't see a way to run out, think about shooting a leave. I read once that pocketing a ball without running out is like killing one of your own soldiers. It's ok to pocket a ball that's doing you no good if you can use it to get shape on another ball. Making all but one ball and leaving your opponent with four or six balls left is suicide. He can easily shoot a leave.
- Find your opponent's weakness and exploit it.
Everyone has at least one. It's just a matter of finding it. Watch your opponent carefully. Does he hit the ball too hard? Can he control the cue ball well? Is he thinking only one ball ahead? Does he have trouble shooting off the rail or over a ball? How does he handle kick and bank shots? Can he be lured into making a shot you want him to make? Does he shoot low percentage shots? Knowing what he can't do is the key to shooting a good leave.
- Never get emotional about the game.
If you feel your heart beating faster, you're going to make a mistake. Stop and take a deep breath. Think only about the game and ignore your opponent. Forget the mistakes you've made previously and concentrate on the future. If you get angry with yourself or your opponent, you've pretty much automatically lost the game and even if you win, you've ruined the fun for everyone, including yourself. Anger is a major weakness.