butternutsquash:
Here is a great tutorial that helps explain Histograms, Levels, and Curves. And if you don't know what those words mean, don't be scared off. Before I read this tutorial, I would play around with the sliders and noticed the changes, but I didn't know what the point was and was mostly stumbling around in the dark.

While looking up references and links for a tutorial on animated icons, I found one specifically for Gimp, which many of you use: Here. I don't use Gimp, so I can't verify the quality of this tutorial. Remember that the size limit for icons is 40 kb for Live Journal (and elsewhere) and 100 kb for Insane Journal.