That's a good start.
You can try playing around with layers (Ctrl + Shift + N in Windows) or duplicate your present layer (Ctrl + J) so you don't ruin your picture in case you want to try painting it over with a brush or apply a filter.
Layers work wonders, and they add dimension.
You can play with opacity too while you're experimenting with layers, it's amazing how things can fall seamlessly into place (especially color hues like the one you made above).
For the lettering, it's good to see that you can play with the blending options effectively. A bit more of practice and you can create lettering similar to Havoc's sig above, and other whatnot.
Here's an example of lettering and multiple layer editing in a solid picture
(This is my sig in another forum... I seldom go online though, so I'm pretty much scarce there as I am here... go figure)