Any projects involving electricity should be approached with extreme caution. Like plumbing, you may be able to pull off minor repairs like changing a light switch or installing a ceiling fan -- as long as you make sure that your power is turned off before you start. You can test the switch against the breaker so you're positive that there isn't a current, or you can just turn off your master switch to be super sure. You should also invest in a decent volt meter so you can test wires for power. But if the repair goes beyond a simple fixture, it's best to call a professional electrician. In some instances, you have to have a permit to get the work done, and a professional will be your only option. Extending or replacing circuits is dangerous business if you don't know what you're doing. One wrong move could burn your house down, and a shock could result in injury or death. There are also building codes that are mandated for safety purposes; not being up to code may not affect you now, but it will if you ever try to sell your home.