[Fins in the Bin]

Buy one of those tick testers a HD that lets you know if there is voltage present. They won't tell you what the voltage is, just that there is something there. Turn off the power related to the lights you are working on, and double check that you have no voltage on each of the wires you are cutting. The only other thing that gets some people zapped is a neutral feedback that should not apply to your switch replacement. 120v in a residential environment is not very strong, unless your walls are metal and you are barefoot and standing in a puddle. I don't even turn the power off when I am doing them, but I wouldn't sugggest that to you yet. Piece of cake on the home improvement meter!