Try making the animal's exhibits more realistic-looking. What I mean is try to make an animal's area look like it's actuall habitat. Let's take a gazelle for example. They live in the savanah, so lots of grasses and fewer trees helps to have a more realistic feel.
Also, try to get some rare or endangered species. Those are the most popular animals, so lots of guests and donations will roll in soon.(Besides, it's good for conservation purposes!)
If you have MM2, building shows also helps, but try some new animals. Start by adopting a less popular show animal, like a beluga, and gradually work your way to a more poular animal, like an orca.
Entertaing guests is a biggie here. Guests like happy animals, so when the animals are happy, the people are happy. For kids, build a playground for them. Most people like animal kiosks and places to rest, so have plenty of those. Tour guides are a great way to entertain those bored guests. JEEP tours are the best way to go.
I really hope these help you, dude!:happy: