Adding a receptacle? Changing a switch? Re-wiring a lamp? Building the ultimate workshop power strip? Be careful friends. Work safe. 

Simply put, don't mess with electrical, unless you know what you are doing. Honestly, it's actually not that difficult, but it's high stakes. Generally you can't see, taste, smell, or hear electricity. You sure as hell can feel it though. Holy cow, you can feel it.

Fifteen years later, I can remember the feeling of 277 volts ripping up one arm, across my chest, and down the other arm when I got caught up on a three-phase neutral carrying a lighting load in a commercial construction project. Luckily, I broke the connection without a heart attack or falling off the ladder. I remember realizing that dude that had been screaming behind me was actually me. That shit hurt. 

120 volts of household current can kill you just as dead as much higher voltages, it just lets you suffer longer, and folks can still recognize you in your casket. Plus, electrical issues can do a heck of a job burning your house right to the ground.

When in doubt, get a professional electrician. If you do, these residential projects are a snap for someone who's trained; it shouldn't cost too much.

Turn off the power. Use an electical tester. Even if you know what you are doing, work it like it's live, even if you are absolutely positive it's not. Because, sometimes, it still is. Don't trust the person who wired it originally. High stakes. 

Research legal requirements in your area before making changes to your electrical system. 

Finally, don't take my word for this stuff, I might be some random idiot on the internet. I'm just sharing how I did it for your entertainment.