You're cetainly on the right track, so forgive me if I'm being obvious or repeating after someone. Right now I think your paintings suffer from being a little on the monochrome side. Or maybe I should say 'objects in your paintings' instead of 'paintings'. I'd like to see a bit more color variation there. Brown lizards arent just varying lightness of brown. There's lots of other colors there, plusr light bouncing around the environment would introduce some more colors, and at the same time help unify your creatures (or whatever you have in any given painting) with their environments.
You're doing good, so don't give up and have some fun with colors - bring more life to your creations.