I have learned:
1: Always buy a little extra fabric, just in case.
2: Some days are better than others for quilting, and it's okay to walk away when things aren't working out.
3: It's ok to say "no" with no explanation needed.
4: Stay away from precuts and stick with fatquarters and yardage; far too many variables and ends up being more work and effort and not worth the "convenience".
5: Don't be afraid to try something different, be it a pattern, color or technique, expand your horizons, you may find a new favorite.
6: Don't feel guilty!