I've been cutting my boys' hair since their first haircuts as toddlers. It's pretty easy really, just get yourself a good pair of clippers. They knew a haircut was coming up as we were in serious shaggy hair territory with rediculous bedhead results. My older boy asked for a mohawk. Sure, why not. My youngest decided he needed one too. I don't think he knew what one was. I made sure to show him a a picture first. He was all for it - "Cool!"
I used a #1 clipper for the sides and a #7 for the middle. Gel keeps it centered in. My oldest didn't want his quite this short, so we did a #2 on the sides and a #8 for the middle. He was also being photo shy, so no pics of that one!