Here is my answer.
1. Challenge yourself to keep learning. Read books, articles, and blogs of all kinds. Stay curious. Look up words or phrases you don't know.
2. Note the writers you like and ask yourself why you like them. For me, it means they're writing in a style with which I resonate. The implication is that I can learn more about writing in my voice by reading that writer.
3. Copy sentences by those special writers and keep them in a folder or a document, which you read from time to time. (I've been doing that since 1996.)
4. Join an editing group, because that helps you de-sensitize yourself and learn not to take rejection personally.
5. Pass on everything about writing you learn. The universal principle is that the more you give, the more you receive. (And didn't Jesus say something about that?)
The best professional practice is to keep learning and not stopping.