When you are working on your skills it's hard to tell how much you are getting better. The improving process is really smooth and you hardly realize that you are actually improving.
Sometimes you can feel those 'Level Ups'. In other words you can tell that you are able to do something what you haven't been able to do before. If you're a beginner you make a bunch of those Level Ups in a short amount of time. But if you reached a certain Level it takes more and more time to get to the next noticeable Level Up.
I guess everybody has experienced the situation that someone tells you that you improved so much and you are quiet surprised about it because you didn't realize it.
One thing I love to do to find out how I improved is to paint over old work of mine. It's interesting to see in which areas you improved most over the years.
I've done it a couple of times now. The painting below is the 2nd paintover of an old painting of mine.
Click here for the progress GIF.
April 2004 first time I painted this image (45min)
July 2004 first paintover (30min)
May 2007 another paintover (60min)