1. Write.
2. Write more.
3. Write even more.
4. Write even more than that.
5. Write when you don’t want to.
6. Write when you do.
7. Write when you have something to say.
8. Write when you don’t.
9. Write every day.
10. Keep writing.

Obviously, writers are readers too; they also analyze and study their craft, in a continual growing process.  But the point here is valid that the best way to improve your writing is to write.   Especially starting out, it’s vital to break through the initial block by forcing yourself to just do it, and hopefully Newton’s law of inertia will take over from there.  But it really does get easier.

To remix Frost: Writing is a hydrant in the yard and good writing is a faucet upstairs in the house.  Opening the first takes all the pressure off the second.