Varied diet, good filtration, regular WCs, proper lighting, understanding the species I keep. To many people and places tend to lump fish into catergories. I treat my fish on a fish by fish basis. And imo you can never overfeed juvinile fish. frequent feedings do more for my fish then one or two large meals. If I can get away with live plants in a tank I load it up! and you can never have to many hideing spots. a fish with an opportunity to hide, but doesn't is a happy fish. and driftwood.. lots and lots of driftwood. or other decor to simulate natural habitats. Lava rock will strip a slime coat, and is a pita to clean. I've found the stuff useless.
But the top of the list is Patience,Balance, and careing. Patience because a tank doesn't cycle over night, 'nore can properly treating a sick fish, 'nore quarantinieng. Balance, in my tank lay-outs, and feeding practices. Careing, If you care about your fish you notice each individual, and can see slight abnormaties in them before something minor gets major more often then not. Even my feeder takes get "cared" for. If my feeders are sick, then my large stock gets sick. It's a circle.
I don't think it is so much "secrets" but these are the things I have learned.
