Tip Seven
Whatever you do, don't use two animals. One is the flamingo, the other is the crocodile. The flamingo never gets satisfied (This happened in my zoo) and they have an extremely short lifespan. The crocodile is very heavily not suggested for mixed exhibits. They will kill anything from their biome (I haven't tried other biomes; I don't think I've ever placed an animal in an exhibit with a biome thats not its own), even Nile monitors (Which are also carnivores).
Tip Eight
You can make your old animals live a bit older. When you think an animal is really old, keep an extra eye on that exhibit. When the action says "Dying of old age", move the animal somewhere else. If you're lucky, it will do an activity before going to die again. Keep on doing this until you're ready to let the animal pass.
Tip Nine
There are some interesting varients that are quite awesome to see. A few that I think are really cool are the two-tusked narwhal (Only works with males; females don't have tusks), the black/white Sabretooth, the white tiger, and the fact that zebras have different patterns in-game. These are rarest in the order from first to last (The two-tusked narwhal is extremely rare, the black or white Sabretooth is a little rare, the white tiger isn't very rare, and the zebras aren't rare at all).
I am Left, also known as Cleft, and I like Tostitos.