I guess before you can learn how to tre-flip you need to know how to land a simple kickflip. The kickflip is one of the harder basic street tricks to learn and you must have a good ollie to be able to land one. The most important parts to landing this trick is your stance and the flick.
There are many variations to how you can set up for this trick and there isn’t necessarily a wrong way, it is what works for you. First, put your back foot on the tail just like you were about to ollie. The front foot should go about 2-3 inches behind your front bolts at about a 45 degree angle near the edge of the board. Many people like hanging their foot completely off, but I feel that it is easier to have the ball of your foot right behind the front trucks.
2. Pop and Flick.
This is the part that takes some practice. Go about your kickflip as you would a regular ollie. It is important to get good pop so you have enough clearance to get your board to do a full rotation. Now, once you start your ollie, drag your front foot up the board as usual then flick your foot down only using your ankle. If you use your whole leg you will probably over shoot it. This really shouldn’t take much muscle to make it spin, so if you are struggling try sliding your foot down and off the board a little more.
3. Spin and Stomp.
Now pull your front foot back enough so you can let the board do its rotation, this really depends on how high you can ollie. Once it comes around stomp the board down just like you were landing your normal ollie. Now you have to be able to skate away to say you landed your first kick flip. I feel that it is easier to land with a little speed, but that is up for argument. You can always get your friends to video so you can compare yourself with the pros and figure out what you are doing wrong.
4. Go Skate!
Here are some helpful videos and Skateboard-City.com has a good tutorial with some troubleshooting if you are having problems.