Originally Posted by sizzle
A good and safe way to start is just start learnin how to ollie on flat-ish areas at the top and bottom of the slopes. Then gradually start doing it while moving slow and then so on.
You are ready to park when you're ready to bust yer arse! lol
Well...although that is true, I'd go with being able to ride flat and ollie as well. Much of park riding involves landing in some fashion from some duration of "air". If you can't land stably, you're not ready for park. And depending on your resort, some have "baby parks" where you don't really need to be able to "kill it in the blues" in order to attempt the features. But again, you will have to land your tricks and ride away stably.
Personally, I do not think you need to "180" before you can do park stuff. You're tricks will just be limited. I know many ppl who can't ride switch and can do many large park features. Unless you're a "natural" at switch, learning to ride switch and "180"s to top that off will take a real long time relatively judging by other's experiences.