Here are a few simple tips to help you:
1) Learn where your circuit breaker switch is, and know which switch does each outlet.
2) You can purchase a simple fluke, greenly, etc... conductivity meter to use for checking for voltage without having to touch or open wires. These "wands" run on typically AAA batteries and a light will turn on in them if they are next to live conductors.
3) If it is safe to access the wires / terminals you can use a volt meter (ac) to check for 120Vac on your line. Ensure your meter can handle upto 120Vac. Place one meter lead on your hot (typically black), and the other lead on neutral (typically white).
Of course if your dealing with a multi-phase system you can run each phase with a common neautral wire. This has not been my experience in residential systems; however, I've not experienced every situation yet.
JW