It's easiest to practice 360 flips off of a little bit of a ledge. A curb can work just fine - I'm not talking about a huge ledge, but just a little extra space. This will give you a little bit more time to complete the flip, and a little more room to move around in.

Once you have a place in mind, get some speed going and get your feet into position.

Now, you want to pop the board, similar to any old ollie or kickflip, except that you want to scoop down and back with your back foot. This is the key to 360 flips - this scoop. So, as you pop the board, push down and back with the ball of your back foot.

This scoop is what makes the board spin.

With your front foot, flick the board like you would do for a kickflip. Don't flick it too hard, and don't really even worry about it too much. If you have your kickflips dialed in, like you should before tackling 360 flips, then the front foot should come naturally. Jsut flick it.

Now, here's the hard part to all of this - you want to scoop the tail and flick the nose at the same time. It should be one motion. This is another reason that being a confident skater before learning to 360 flip is a good idea - you need to be comfortable with two feet doing two completely different things! This part can take some time to practice and figure out - that's OK. I don't know anyone who learned to 360 flip on their first try. Or really, their first dozen tries! But you can do it - just relax, visualize it before you go out and try it, and practice!