The possibilities are nearly endless... Keep the size of the fish in mind and provide plenty of plants and hiding spots. And avoid overly aggressive species such as most Serrasalmus Piranhas, certain Snakeheads, etc. It'll create a ****ty environment and the other fish will mostly resort to either being reclusive or also becoming overly aggressive.
Think of predatory fish like dogs. It's all about memories and experiences. When a dog goes bad, it's bad, and it'll stay bad, unless you're the dog whisperer. Or fish whisperer I suppose.
It's all about creating a healthy environment for your fish. Live plants and other decorations will help with this as well as not overstocking. You'll see your fish at their most active, and their personalities will really come out. This is especially true for Bichirs. Also Ropefish! Get some Ropefish they're awesome