Okay, it would really help if you can fakie ollie already (obviously). And if you can do a regular 180, it helps a ton, but it's not required. A lot of people find half-cabs easier than regular 180's, but I think these look a lot cooler.

A Half cab is just a 180, but in fakie position. It is a half cabalerial (which is a 360 in fakie position).

Start with your feet in a fakie ollie position, but some people like to leave their heel hanging off a tad, and others like to slant their feet a little. It really depends on preference.

Now, before you pop your ollie, start to spin your shoulders and upper body. When your body is about to hit 90 degrees, pop the ollie, and your feet will follow around with your shoulders.

Around this point people usually can't keep with their board. They let their back foot come off of it, but not you, your going to stay with the board and land it first try, right? Wrong. If you land it first try, then good for you. But if you can't then it's normal, and go back and try it again. Stay with that board.

I've noticed that trick tips on a website don't help as much as an actual person beside you walking you through it does, so try to get one of your friends who knows what he's talking about to help you. This trick is quite easy, it's all in the shoulders.