"The best advice I can give has little to do with actual writing; it has to do with thinking about people. I recommend that you practice creating fictional characters by trying to describe, privately, the people in your life. See if you can describe their characters without being so general that they could be anyone. Then check back in a few months. If your description has radically changed, you have a ways to go. You aren’t yet seeing other people as fully fleshed out others, but are mired in your own relationships with them. When you can describe people in ways that are both meaningful and consistent and survive the vicissitudes of your moods, then you know you’re getting somewhere."
- Adelle Waldman

Emotionbending: Ultimate Writing Resource List

a massively extended version of ruthlesscalculus’ post

General Tips

Character Development

Female Characters

Male Characters

Tips for Specific Characters

Dialogue

Point of View

Plot, Conflict, Structure and Outline

Setting & Worldbuilding

Creativity Boosters* denotes prompts

Revision & Grammar

Tools & Software

Specific Help