CD's fun Artistic copy Ninja training guide. Based on my own experience in copying... (I might color a few if i feel like it)
My own style falls somewhere in level 40-50, in the normal anime range. My copy skill is pretty high at this point if i want to spend the time for it...
How to use:
Use the chart to compare the level where you are at in terms of your own style, and your ability to copy other people's style.
+ When to move up: If you have been copying simpler style, and can do them well, move up.
+ When to move down: When you have trouble with more complex styles, try some really simple lower level ones, you might get a few lessons you have never learned before to apply to more complex styles!
+ Sharing: You are allowed to print this, to use this chart to show anyone who need to know where they are on practice level. As long as it's non-commercial.
+ Benefit of copying: It forces you to get rid of your usual habits and learn to adapt something new, and learn the observation skill of the artist at higher level than you.