To quote a writer, Neil Gaiman,
How do you do it? You do it.
You write.
You finish what you write.
...
Writers groups can be good and they can be bad. Depends on the people in them, and what they're in them for.
On the whole, anything that gets you writing and keeps you writing is a good thing. Anything that stops you writing is a bad thing. If you find your writers group stopping you from writing, then drop it.
The other thing I'd suggest is Use The Web.
Use it for anything you can - writers groups, feedback, networking, finding out how things work, getting published. It exists: take advantage of it.
Believe in yourself. Keep writing.
http://www.neilgaiman.com/FAQs/Advice_to_Authors
tl;dr? Like any skill, you just write, and write, and write, and read, and think, and practice, and write some more, and get feedback, and think about your stories, and write some more.