I actually want to do the samething. My advice would be to not give up even if some of your ideas are turned down by some people continue to pitch them out and whatnot.
Read (but not too much)
write a lot (ideas, scripts, whatever)
Watch Screenwipe http://www.youtube.com/profile?user=Xthemusic (start with the first episodes... sometimes it's UK-centric but it's all about how television works)
experience stuff