How to get good at writing? Write.
Julia Cameron wrote a book called The Artists' Way that has awesome advice for letting your inner creative out.
And a couple of the things I've picked up are:
• You take care of quantity and let time/experience take care of the quality.
• You can't get better and look good at the same time... be happy to suck for a while.
• Keep your butt in the chair and write.
Good luck!