1) Practice your craft. Do small challenges, participate in contests, use prompts and do it all with the idea of getting better.
2) Learn how to take criticism (not like take it with a smile kind of stuff.) Learn how to process what you're being told and assess it for yourself. Then apply it, or don't accordingly, but always be grateful for the opportunity to be introspective and to grow.
3) Be practical. Being creative is amazing, but it's not always what makes the world go round. Be able to see all aspects of your craft even the boring ones. Keep economics, logistics, and legalities in your peripherals at least. They may not be exciting, but they're just as important as the art, and the people who do have to focus on those aspects will be grateful for your willingness to see their side of things.
4) Know what your goal is. I write for the love of it and I have a full time career outside of writing. What that means is, I never have to compromise to make a profit and I have to prioritize my job over my writing sometimes. If my goal were writing to make a living, that would change both of those facts.