My Top Ten Tips:
10) Take acting classes. It may sound weird, but having the ability to role-play characters is a major advantage, and doing it by getting into the character's mind is a major plus.
9) Study script-writing. Look at more than just the format; consider pacing, beats, and why the three-act structure works, as well as proper escalation.
8) Take some journalism classes. As a writer you need to learn that less is more, and this is probably the best way to do it.
7) Spend some time in a bar or a park. You want somewhere busy, where people are talking to another, the busier the better. The idea is that you're going to need to learn conversation, and where better to learn than where people do a lot of talking? There's a reason so many writers have a reason for being drunks...
6) Kill your darlings. If something is cool, but it doesn't fit with what you are doing, then don't be afraid to not use it. The cool scene may end up being the albatross that kills whatever you're working on. You can note it, and use it later, but don't feel obligated to use everything you write.
5) Character>Plot. Don't force your characters into doing things that they wouldn't do. If your plot requires that your villain make a really stupid mistake, give him a realistic reason for making the mistake, like his girlfriend is breaking up with him or he has some serious bad news to deal with.
4) Avoid gratuities. Always tip your waitress, but don't use sex, violence, and language unless you have a reason, and shocking people isn't an acceptable one. John Woo should be your role-model, not Quentin Tarantino. Now, if you're making an erotic comic, use all the sex you want, but otherwise try to avoid it.
3) Read and watch. Any arguments re: "but then you don't have any of your own ideas" are BS. You would be surprised when those bits of trivia come in handy. Also, you need ideas to get your own. And watch the bad as well as the good; you never know what diamonds you'll find in the mud.
2) Have fun. Don't do this if you see it as a chore; just remember to take it seriously.
1) To thine own self be true. If you're doing this to pick up girls, or impress people with your ability to write, this is the wrong place. Write because you need to do as badly as breath, not because you want to get rich or laid...
If it helps...