Here are some links to things that have helped me:
Alliance of Independent Authors (ALLi) – the professional association for self-publishing writers
Advanced Twitter Strategies by Ian Sutherland
Opening up to Indie Authors by Debbie Young and Dan Holloway
Reader Magnets: Build Your Author Platform and Sell More Books by Nick Stephenson
How to Make a Living with Your Writing by Joanna Penn
Sell Your Books!: A Book Promotion Handbook for the Self-Published or Indie Author by Debbie Young