It could be a good idea to at least film some very very low budget short films. Just to get yourself behind the camerah and into the directors mind set. i wrote a lot of scripts when i was in highschool and its not entirly different shooting them and making them into a movie but all the practice you can get is really the best thing. No sence in waiting to make your first movie a full length without mush real past experince. Shoot as much as you can. Here is an excample of what i mean my friends and I did this short film.

http://www.metacafe.com/watch/1064920/chained_up/
It also helps to see what people have to say about it. but metacafe and you tube arn't the best sites for intelegent opinions post it on forums like this and you'll get educated and good critiques and advice. good Luck man!!