If there is one thing I have learned about park/pipe skiing is that there is no "proper" way, just personal style. therusty pointed that out to me on another thread about 3's.
If you have already got 180's down to both directions, that is a great start. Figuring out which direction to spin is very easy.....learn both ways. Many park rats that I have taught can throw down 9's right side....but can't 3 left side, so learn to be versatile from the word go.
When you want to progress to 3's, go to the bottom of a halfpipe where the deck comes down to meet the flat and forms a triangle. When you want to spin left you should hike the left wall and drop in (look uphill to ensure you do not cut someone off) and carry your speed to the triangle.
As you approach the lip of the triangle flex ankles and knees slightly and pre-wind your upper body to the right. Also make sure you have weight on the inside edge of your right ski to give you a platform to spin off of.
At the lip (be patient) you need to extend ankles and knees to get pop, powerfully unwind and as your hands come back to neutral lock your lower body with your upper body and look around with your head. Keep shoulders and hands level with horizon to ensure you do not cork your spin. Things may get blurry but stay tight and focused. Landing will be gentle as you are not very high off the ground.
You may or may not get all the way around to 3 but that is why you are at the triangle. If you only get 270 you are still pointing downhill so it makes it easier to ski out of an under-rotation without penalty.
When you want to try the other direction just reverse all the directions, then try switch 3's they are real fun too.
Trampoline work is very helpful and if you are lucky you can find a cheap one online. Mine cost $35 on craigslist, no brainer!