Here. I have noticed alot of people asking for help on 360's and spins in general. Instead of just giving them one or two word replies I thought I'd give you a complete guide. Hope this helps you out.
The complete guide on How to do 360's
The most important things to think about when doing spins:
1. Where your head looks, your body follows. If you stop looking over your shoulder, your body will stop spinning. Ask yourself if you are keeping your head going or are you stopping your head before you get there?
Also, if you get thrown off axis, make sure your head is looking straight over your shoulder.
To demonstrate this, go out on the trampolean or just jump off the ground. Now, try doing a 360 while looking straight up at the sky or down at your feet. It may feel really weird and even throw you off axis. This is because your body follows where your head looks. If you want to spin straight, make sure you are looking straight over your shoulder and that you aren't throwing your head way off to the side in an attempt to whip it around.
2. COMMIT. Tell yourself before you go off the jump that you are going to do it no matter what. Chickening out or going halfway is not an option. Visualize what it's going to look like in your head and picture what you need to do to pull it off. You have to commit. Also, tell yourself what's the worst that could happen? So what if you screw up, you might crash. But if you are throwing it off of a smaller jump and crash, you are probably not going to get hurt. Big deal, you might slide out or land backseat. But you will be fine. Do whatever it takes to commit.
3. How is your stance before you are off the jump? If you start yourself off wrong, you are going to land wrong. One of the most important things with spins or with any trick for that matter is what you do BEFORE you are in the air.
Think about it. What are you doing right as you are going off the jump. Are you leaning back? Are you starting the spin before you are off the jump? If you lean back before you are off the jump, that means you are going to have to fight to stay on axis throughout the whole trick (which is why many people flail like crazy when trying 360s). If you're spinning before you are off the jump, what is that going to do for your balance? That means you are probably going to be thrown all crazy or catch an edge.
I dare you to try leaning way to the side, looking over your shoulder, and putting most of your weight on one foot as you go off a jump for a straight air. Hah, I guarantee that you will get jacked up. So why should it be any different if you are spinning?
Keep a solid stance. Your hands in front of you, pressing forward on your boots with your toes. Equal balance on both skis. Don't be afraid to widen your skis a little bit. A slightly wider stance is stronger.
4. Shoulders. Bringing your shoulder close to each other will make you spin fast. Have you noticed how figure skaters bring their shoulders very close to each other as they go for huge spins with one foot of air? Opening your shoulders up and keeping them far apart slows you down. Think about that with spins.
5. Pop. Popping off the lip of jumps is your new best friend. Make sure you are popping and not just riding right off the lip of the jump. Popping will give you more height, more air time, and will help keep things much smoother and together.
For your first time, you can hold your hand out in front of you as you spin. If you are spinning to the left, you can keep your left hand out like it's going to punch. As you pop off the jump, you can look over your shoulder to the left and look at the end of your hand all the way through the 360. This could help you stay straight and keep it going.
So, let's put this all together.
Before you come up to the jump visualize in your head what you need to do to do the trick. Tell yourself that not committing to it is not an option. No matter what it takes you will pull the trick around. Picture yourself doing it. Now, go as fast you normally do into the jump. I know you might be nervous because you are doing a trick now, but you want as much air time as you can get. Makes it easier than having to chuck it off the ground.
Keep a good strong forward stance, pressing hard on the front of your toes. Your skis can be wider too. As you are going off the lip of the jump, POP. Now, gently look over your shoulder and keep looking until you've pulled the whole spin around. If you are spinning to the left you can bring your right shoulder in close to you if you are not spinning fast enough. Pull it around, stomp it and then ask that jump who is it's daddy?