I used to assess my skills based on these parameters, but they might be slightly shallow measures for a seasoned dev.
- Quality: Is the quality of your current project better than the quality of your previous project?
- Time: Did you accomplish task X in time Y when previously you would have taken time Z to accomplish X ( where Z>Y)?
- Design: Are you able to structure your code better than you would have before?
- Errors: Is the average number of mistakes you commit on a decline?
- Clarity: Do you have greater clarity in your thought process while taking on a problem?