How big is the tank/how many gals does it hold?
If i were you i'd move the big rock pile and split it in two, moving each separate half to the back corners of the tank and get the plants to grow through the rocks.
I don't think the blue background does much justice to the type of ornements/plants you have in your tank, if you have to have a background i would go for one of the those underwater-photo-of-river-stream-plants type of ones; it would fit much better into the natural look of the tank and give the impression it is bigger and more planted.
As for plants, maybe add some "myrio filigree" and/or "green hedge", no? You already have quite a few broad-leaved plants so why not go for some finer ones too add a bit of variety?