First, read as much as humanly possible. Read everything—fiction, nonfiction, history, biography, poetry, science, everything possible. You can't read everything that's been written, but you can try.
Second, write as much as you possibly can. Write stories or poems. Keep a journal, keep a diary. Write notes to yourself, or whatever comes into your mind. It doesn't matter what it is. Don't even worry whether it's any good or not. If it's bad, throw it away. Nobody will ever know. It's a matter of practice, writing, the same way that a pianist practices the scales, or a ballet dancer who constantly exercises. Simply do it continually. It really does help. It's a matter of getting fluency, of not being scared of blank paper. It starts a good habit pattern. Writing every day, even if you have to throw out what you've written, is marvelous practice. It builds up the kind of discipline you need to keep on working no matter what else happens.
Third, be as alive as possible. By that I mean be open to all your experiences. Look at things carefully, listen to things, look at the world around you. And be sensitive and responsive to it.
Oh, and there's one more thing. Hardest of all. Be patient. If you're patient, you can finally do everything you want to do. This applies to everything. But that's hardest of all.