If you want to be a writer, you must do two things above all others: read a lot and write a lot."-Stephen King
Here's the thing about writing no one ever tells you when you're starting out and probably still in school, ensconced, perhaps in a nice cozy writing program: in the real world writing can be a pretty lonely occupation. And it can often take years before you'll have anything in the way of tangible, earthly evidence to show for your efforts.
Still in? Then get to it. Write, write, write. And read everything you can get your hands on, too. Experiment with different authors and genres. Stretch yourself beyond your comfort zone. Go as far as you can without needing a cranial chiropractor.
If you're out of school, you might want to find a writing group or workshop to join. I've been a member and facilitator of such workshops and always find the connections, criticism and companionship inspiring. Even if the group is small or you don't find the critiques particularly sophisticated, you'll get a boost just by sharing your work. Heck, for some folks just leaving the house and talking to people is enough reward.
Seriously, the best thing a supportive workshop or group can do is offer you a space to be heard, encouraged and held accountable. Yeah, I said accountable. Most writers fall prey to procrastination, but with a group's weekly ( or bi-weekly) deadline approaching, you may be pleasantly surprised at your own output.
Spend your time outside the group writing and re-writing, borrowing tricks and insights you picked up from your colleagues. Don't forget to leave some time for reading, too. You'll want to unearth wisdom from professional journals and blogs to share with your fellow writers at the next session. And immerse yourself in fiction or non-fiction that ignites your passion for craft.
Do it again the next week. And the week after that. And so forth until you've actually cultivated something resembling the write stuff. You might even have something to show the world. And you'll more than likely have begun to enjoy the solitary writing life just a little bit more.
Cheers and onward.