NaNoWriMo is coming up this next month. If you haven't done it I would suggest that you give it a try, if nothing else then that writing a story of 50,000 words in 1 month is excellent practice for writing under pressure. Besides that, any excuse to practice your writing is good. My advice if you wish to write would be the following:
Write, write, write, and write some more. It doesn't matter how good it is initially, you need to write as much as you can, find your voice, it may be tempting to follow "rules" to a 't' but you need to have your own voice, that is very important too. NaNoWriMo gives you a great excuse to practice your writing, and if it turns out to be a horrible story, who cares! You're that much the wiser of what doesn't work for it. Writing isn't easy, it is a painful process with a lot of junk produced before you get to the good stuff. It's kind of like digging for treasure, there is probably going to be a whole lot more dirt then treasure, but you can't get to the treasure without first digging up the dirt. Writing is an adventure, you never know when that crazy idea you put in your NaNoWriMo novel might bring forth your next spark of literary genius.
Second piece of advice: Read, read, read, and read some more. Nearly or as important as writing, reading as many books as you can get your hands on will help you write better. Believe me, it is very important. Ask just about any of the most successful and/or best writers out there, chances are pretty high that they are huge readers. Try to read as wide a variety of genres as possible, even things you normally wouldn't like that much. Read outside your comfort zone. If you're a fantasy fan, try picking up some Austen or Dickens. If you're into romance novels, try reading a dystopian science-fiction novel.
My third piece of advice: I don't see this one very often, in fact I don't remember ever seeing it in a writer's advice article. Study the art. Study what it is that makes great fiction great. Learn about why things like Shakespeare move, inspire, and occasionally even transform us. Learn what it is that causes some books to impact the very soul of the reader. Learn about symbolism and what it is and isn't. Study genres, even those outside your particular niche, learn what it is that defines them. Be aware that the culture is Post-Modern, and that like it or not, you are probably going to be writing for Post-Modern readers, it is not a bad idea to study Post-Modernism. It is the language of the culture, if you're going to talk to the culture, you need to at least know the language. Study the art. Learn about literature, both classic and modern. With rare exceptions, great writers don't usually just sit down and think up a fantastic story, there is an art to it. Learn it!