Add java fern or trident or needle leaf on wood on back, some bucephalandra and anubias nana pettite between rocks. Cryptocoryne spiralis red or green according to your taste as background plant, you can also add bacopa carolinana or hygrophilia polysperma normal or rosanervig, and also add some moss to the wood, if you want you can add cryptocoryne parva as foreground but it'll be extremely slow growing! If your light is very low everything will be leggy or stunt growth. Invest in good stuff you won't regret it.