I'd suggest doing some non-pixel-art. That helps me, at least. If you can't draw it on paper, you definitely won't be able to draw it in MS-Paint, right? XD
If you're looking for simple things to pixel, start with basic shapes, maybe? Spheres, cylinders, and such. Again, if you can't pixel those nicely, you don't have much chance at doing something more complex like a tree or something like that. Starting super basic and working your way up is probably the fastest way to learn...
Then again, it's probably also the most boring way, too. Do whatever suits you, heheh.