Tools

* Use tools for their intended purpose. A screwdriver is not a chisel, pliers make a very poor hammer and so on. The risks are not always obvious, but as a general rule tools were designed with a particular job in mind and perform inferior or unsafe when used for different jobs.
* Keep tools sharp ! Whether it's a saw, a chisel or a knife you need to use *much* more force when they are blunt than when they are sharp. Then when you lose grip of the tool or the tool slips on the workpiece all that force will be liberated, and you will either go crashing into the workpiece, or you'll hit yourself (or some bystander) with the tool.