Assuming you have a big enough tank to house an adult Oscar I would somewhat agree with the other suggestions already posted. However I personally don't care for barebottom or black substrate. I prefer gravel just to avoid any of my filters picking up any sand. Black substrate tends to look dirty all the time to me. I like a more natural color. I wouldn't make the tank completely void of all decor but keep in mind that large items displace water and detracts from the stability of having a large tank. A single medium size piece of driftwood is nice to have and gives them something to take cover behind if they happen to feel a bit spooked (like during water changes). I would avoid 3D backgrounds & anything else easily destroyed. Aside from that good bio & mechanical filtration is a must. The smaller the tank the more you will need.