I'm still working on these since I don't see terrain parks very often.
Find a little kicker/table you are really comfortable jumping on. This stuff is way easier when you aren't scared. Lose poles if they get in the way, you don't need them for your first few tries.
So anyway, head towards that jump at whatever speed works. When you are close, start twisting your body whichever way you want to spin. Hips, torso, arms, neck, head. By the time you get to the edge of the jump, you should almost be looking backwards. Pop off the lift, and keep looking around. You will be spinning, and after about 200-250 degrees you should see the landing if you neck is still twisted.
Keep looking at that landing, and let the rest of your body untwist and come around. If you time it right, you should have enough time to bend your knees a little bit, and stomp the landing.
If you crash the first try, you will probably realize it doesn't hurt much and be even more pumped to go at it again.