All it takes is a set of clippers from your local beauty supply store. They start at about $25 and last for years. It's nearly fool proof! I say nearly, because it is fairly easy to learn, but there is one caveat...
You have to pay attention.
That seems simple, but a long time ago (before I'd honed my haircutting mojo) I cut a straight-up bald spot in my brother's hair.
I had already finished his cut and it looked pretty good, so I was just trimming up his neck. But I noticed a spot on the back of his head that I'd missed and thought, I'll just run the clippers back over and cut those stray hairs. Unfortunately -- with no attachment (because you have to remove it to shave the neck) -- I shaved a bald rectangle out of the back of his head!
Well, my brother wasn't pleased, nor was he ready to embrace a cue-ball head, so I had to take his cut pretty short and he used a dark eyeliner pencil to draw it in until it grew back.
Don't let this story scare you, it really is easy to do.