I'm hardly an expert (just starting out myself, actually) but I did notice in your dragon drawing that the brushes you used to color were primarily soft-edged. When I learned to use the default brush in hard-edged mode and tweak the brush settings to make opacity change with pen pressure, my feeble efforts took on a new life.
I've also found for myself that less seems to be more as far as brushes are concerned. It's probably unconventional, but I
picked up this set at Imagine FX and keep finding great use for it, tweaking the brushes to my needs. Brushes are great, but too many choices make my head spin when I'm trying to concentrate on the expression of my work.
I've found it useful to have line art on a separate transparent layer so I can paint above and below it at need. To have it on the canvas itself is frustrating when I need a quick change. It's also useful, when painting, to separate broad areas (sky, character, foreground objects) on separate layers so that once you have the shape defined in a solid block of color you can lock the transparent pixels on that layer and paint within the lines.
At first I thought I had to learn all of the filters, too...then I learned the trick of using texture brushes and adjustment layers/layer masks to get much more natural effects. The eraser, too, can be an amazing little tool for subtle effects.
Like I said, I'm just learning too! But hopefully some of this might help.