Practice every opportunity you get — it’s all practice
Writing is a muscle. Just as with every other muscle, to strengthen it you need to practice.
At times, getting the words out is hard, even for professional writers. Only practice makes writing easier. If you need to write for your job, set aside 25 minutes every day, just to write.
Writers know that writing can be fixed. Stop trying to write well. Write anything… just get something down.
I've started a new "how to write" series on my Creativity Factory blog.