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