I don’t pretend to know it all, but here are some tips that spring to mind. They worked for me, they might just work for you.
1) I believe that my work was given a fair hearing from editors dozens of times before it was good enough, or marketable enough, to be published. You will get those opportunities too. Make sure that your work hits the spot.
2) Rejection hurts. Use it to focus your ideas. I wrote a whole novel where the hero’s unsuccessful quest was a metaphor for my own desire to be published.
3) I had an underlying reason to persevere. I felt that writing was the only thing that made my life make sense. I think you need that to get through the tough times.
4) Use music to get yourself in the appropriate mood for a scene. Sad, hopeful, wistful etc. I collect songs like that. Ethnic music can help when writing of other cultures too.
5) I got an agent first. That took me five years, but his percentage has been repaid many times over.
6) I always use friends as first readers. They don’t necessarily give great advice (sometimes they do) but usually just the manuscript getting ‘out there’ spurs me to think of ways to improve. Even the amount of time it takes them to read it tells me something. Friends who simply give you praise serve a purpose too. You need positive reinforcement at the drafting stage.
7) Don’t be too much in love with what you do. Be critical. Then critical again.
8) Keep reading, particularly in your genre. Reading helps you remember that the most important thing of all is to be interesting. You don’t have to change the world, (though I’m always trying).
9) Observe other people. Keep a journal. (I use my phone these days). When you’re at a bus stop describe the people there while they think you are texting. You’d be amazed the colour and detail you can transfer to your fiction.
10) Imagination can get you only so far. Keep drawing on real life. Hold up a mirror. Use realism even in fantasy.
11) Don’t look down your nose at any other writer, no matter what the genre.
12) And always work on the assumption that your readers are at least as smart as you.