Listen to that little fella on your shoulder
When you hear that voice in the back of your head saying, "this isn't right," listen to it and rethink the operation. Rehearse an unfamiliar cut first, without any spinning steel. If you feel uncomfortable with it, jig-up to make it safer, or find another way.
Inspect your tools
Check every tool before use, even if you were the last to use it: Look for debris near the cutterhead or blade and any loose or misaligned parts that could become projectiles when you turn the tool on. Keep blades sharp and clean: Forcing a workpiece through a dull and dirty blade increases the risk of a hand slipping (and may cause burns and tearout on your workpiece, too).
Watch where you stand
Never put your body directly in line with the blade when making rip cuts at the tablesaw: If the board kicks back, it's coming straight at you. Also, never place your pushing hand in direct line with the cutting motion, regardless of the tool.
Tug the plug
When not in use or during blade changes, unplug power tools or, if the tool has one, remove the safety tab from the on/off switch. This prevents both you and shop visitors (young and old) from accidentally turning on a tool. The same principle applies to pneumatic tools: When adding fasteners to a nailer, always disconnect the air hose first.
Stay mentally sharp
Get comfortable, but not too comfortable, with your tools. When a project requires repeated cuts for identical parts -- making the same cut 20 times -- your mind can wander. Stay focused. Never walk away from a tool when it's running and always wait for the blade to come to a complete stop before reaching for cut-offs near the blade.
Use pushsticks designed with plenty of surface area in contact with the workpiece; they hold the board down while keeping your hand several inches from the blade. A pushstick doesn't have to be pretty, complicated, or expensive -- the shop-made one shown consists of just scrap 2x4 with an MDF heel. Keep a pushstick at each tool station and always within easy reach.
Keep it clean
If your shop has a layer of sawdust as thick as urethane on a gym floor, that dust presents a slipping hazard. Sweep it up. Also, dispose or store loose cutoffs and tools not in use. Clear off machines before use and make sure there's nothing that may shift into your cutting path or the blade during the machine's operation.