Change the gravel to natural sand (playsand or similar), plain black background, bogwood/mopani, natural looking plants (real or fake)... Something along those lines.
imo natural is best, i'd get rid of the blue gravel and fake plant background and replace them with natural coloured gravel and a plain blue/black background, then you'll have a good basis for making it look nice.
i'd then work on finding out a bit about plants and get some nice easy to care for species in there along with some hardscape (wood/stones). i think just putting a few larger pebbles scattered in amongst the gravel looks nice, less uniform and more natural