Read the directions. Before using any electrical equipment or chemical, consult the owner's manual or instruction labels.
Dress for the job. Wear gloves, shoes, long pants, a long-sleeved shirt and, most important, safety glasses or goggles, and hearing protection, when appropriate.
Handle tools properly. Have great respect for saws and drills. And don't use the wrong tool for a specific job -- a chisel as a can opener, for instance.
Keep children and pets safe. When you're using power tools, including lawn equipment, or chemicals, ban children and pets from the area.
Don't leave power tools unattended and plugged in.
Use your head. Overconfidence is as likely to cause an accident as inexperience. There's no shame in seeking help.