1) Write. Keep writing no matter what. Writing is like a muscle. It has to be used to develop.
2) Your writing will change as you do. Your voice will evolve as you grow, so accept that your first book will be very different from your tenth or even twentieth.
3) Be open to suggestions. Reviews (good and bad), beta readers, editors, and fellow authors can all help you become a better writer. Some things may not be what you want to hear but listen. You may hate having to change something in your manuscript but try it and see what happens. You can write in a bubble, but you can't publish in one.
4) Write what you want to write, and don't follow the trends in genres. Writing something because you think you will capitalize on whatever the hottest genre is will turn out to be a mistake. What is hot today, could have turned cold by the time you publish, so write what you want to read. Chances are, you will find readers who want to read it, too.
5) NEVER, EVER GIVE UP!! The only person who will believe in you and your book IS YOU! Accept that there are days you will want to walk away, but always vow to keep going.