One of the more widely-known art memes floating around DeviantArt and even theOtaku is the "year in review" sort of meme. For sake of a visual, I've filled one out for the past three years. This is my most recent version:
It's pretty simple: Each month, you put in what was your best piece, and at the end of the year, you have a visual timeline in an easy-to-reference format. It's a good and simple way to see how one has grown over the course of the year.
But on the other hand, it might not be the best way to see true growth. While people sometimes make huge leaps and bounds in the span of a year, that is often not the case. We simply need a longer span of time to see actual difference.
I came across a meme a couple years ago that does just that. It's the '03-09 improvement meme, which basically forces you to fill in art from a long time ago up to the present. I'm a pack rat and actually have stuff from 2003 (and earlier) - stuff I made when I was eleven. Now that...that's embarrassing.
Even worse, I'm going to link you to it.
I've been updating that the past two years, keeping it current and reminding myself that I have come a long, long way. Seriously guys - it's encouraging. It gives you the chance to look way, way back and then immediately jump to the now. Even the year-by-year differences can give you a totally different outlook on how you've changed and evolved.
We are our own worst critic. And sometimes, we can really beat ourselves over our art. I mean, I do, all the time, and people really get annoyed at me for that. So to have something that lets us see actual progress is uberly encouraging.