Once in a while it happens to you, me and every other aspiring comic book artist. You put down the pencil for a week or two only to get back to the drawing board and find those phenomenal drawing skills of yours are now a little rusty.
That's because drawing is like a muscle. The more you do it, the more magnificent your skills become. Skip drawing gym for a weak or two and before you know it you're going limp. It's not that you've lost it, you're just not running at full capacity.
In order to remain at the cutting-edge level of drawing performance, it's important to set aside that special one on one time with your pencil and paper, even if it's for an hour or two a day, to keep your skills sharp.
Here's some weights to try on for size.
This site holds an entire library of photo references you can use to study up on your anatomy, lighting, and rendering. The dynamic lighting set ups and poses are more then enough to ensure you'll learn something new each and every time to add to your treasure chest of drawing know how.
And since my drawing hours are presently dwindling, you can bet I'll be tackling a few of these myself shortly.