Plant anubias nana petite in between the rocks. sprinkle some smaller crypts throughout. Plant some vals in the back left, maybe java moss on the branch and maybe some ludwigia in the back right. You could get some dwarf chain sword for the background and some marsilea minuata or hydrocyle sp japan for the foreground as a carpet.
If you want to use some branch you found you could scrub it, bake it/dry it, soak it and put it in your tank once the tanins leach out.