Basic Home Repairs - Safety First!
There are two types of people who end up injuring themselves when making home repairs - those who blindly proceed without first thinking the project through and those who have done this type of project so many times that they don't pay attention to what they are doing. Your high school shop teacher could probably tell you stories about students injured becaues they were fooling around (while neglecting to mention their own injuries caused by a lack of attentiveness. The moral of the story is: Think about what you need to do in advance and pay attention to what you are doing.
Before starting any project, take a few minutes to analyze where you will be working, what you will be working on, and how you will be working. If you are working with the plumbing, make sure you know where the nearest shutoff valve is as well as where the main house shutoff is. If you are working your electrical system, make sure you know which breakers/fuses control the circuits you are working with. When drilling, nailing, cutting, or digging, make sure you check your area first - failing to check first could lead to serious injuries (not to mention additional repair projects and/or expense).
Common Safety Checks
Don't drill blind - Before you drill, nail, or screw into a surface, make sure you know what is behind that surface.
Use the right tool for the job - If you need a hammer, get a hammer - don't try to save yourself a walk to the toolbox by using some other tool not designed to do the job.
Shut it off - When working with an electrical circuit or appliance, shut the electricity off (at the breaker/fuse). When working on the plumbing, close the nearest valve (if any). When working in areas where there is no shutoff (i.e, drain lines) make sure nobody is going to use the line until you are through.
Keep it is off - Lock it out or leave a note so that nobody will come along and turn the power/water back on until you are done.
Verify it is off - Don't trust that every valve, fuse, or breaker is labeled correctly. Check to make sure the power/water is actually off before starting to work.
Know where the main shutoffs are - Know where your main home electrical, water, and gas shut off's are just in cased something goes wrong.
Know where your "emergency" equipment is - Follow the Boy Scout Motto: Be Prepared. Know where your fire extinguisher, buckets, towels, etc... are just in case you need them quickly. Keep your phone handy as well in case you need to phone a friend. Also keep some basic first aid supplies around - even the best handyman occasionally hits their thumb with the hammer or cuts a finger.
Know (and admit) when you need help - If you get into a jam don't hesitate to get help - it is better to give your friends something to rib you about than to compound your problems.