I'd like to learn

[Vipershark]

I agree; you're a pretty good artist. One technique I've found works is to draw a sketch, shrink it down, then pixel over it.

Pixel-overs (a fancy word for tracing) might be all right when you're just starting to learn to sprite but they're by no means something that you should regularly put into practice.
They have their uses (in cases where you need to turn art into sprites for whatever reason) but they won't help you create custom sprites. They shouldn't be relied on.