The following are not "cheats" but simply tips on things I believe I have observed while playing the game. I make no claim to their infallibility or otherwise, nor have I been on any forums where Zoo Tycoon has been discussed. If you want to find out how the game seems to work yourself, then ignore these. On the other hand some of them may save you some frustration.
Personally I find the following animals in the basic game to be extremely easy to house:
The hardest ones to house properly and keep happy include, in my experience:
Don't underestimate the importance of creating extra income for your zoo: gate receipts alone are normally not enough to keep you afloat, let alone add on new projects. The following are really the minimum you should consider:
In a big zoo, you may be able to get away with more than one gift shop, restaurant and/or compost building. However, you should check the extra buildings to make sure that people are in fact visiting them (well, all right, not the compost building, admittedly), or else they may be persistent loss makers.
Staff do eat up a considerable amount of the income you generate. There is no getting away from this, and therefore you need to have a strategy.
As a rule I allow one zookeeper, marine specialist or scientist per three enclosures, four at most. Bear in mind that it takes the staff member time to visit each enclosure, and the longer he or she is between enclosures, the more likely the animals are to become hungry (and if they get really hungry, you will get the warning message and your visitors will notice). You can be smart here and arrange the gates on neighbouring enclosures so that they are all reasonably close together, then allocate one staff member to three or four enclosures that are closest together. This works quite well.
I have not yet found a great deal of use for guides, although I am trying to establish whether one can use them to shepherd reluctant visitors to exhibits that you want them to see but which so far seem to have been neglected by the hordes coming in through the gate.
Maintenance workers should not be neglected. As you can get three of them for roughly the same cost as a zookeeper, they are cheapish at the price and perform vital functions, the most vital being the maintenance of fences. Without this, you can expect an animal escape sooner or later, and if it is a Tyrannosaurus Rex or Velociraptor, then watch your ratings plummet. You will also need at least one maintenance worker to go round disposing of rubbish, which mounts up surprisingly quickly and looks unsightly (not to mention causing a drop in ratings, I believe). If using Marine Mania, make sure at least one of the workers is also repairing the filters.
The Dinosaur Recovery Team is quite "sexy" but also hugely expensive, and I have rarely bothered with it.
This one is really a no-brainer, as you will greatly benefit from having at least some of the benefits acquired from putting monthly money into these programmes. However, if you are playing one of the scenarios then you need to be selective: opting for all of the programmes will mean that the one you need to help you win the scenario will be quite slow in coming online. For instance, if you are playing the Big Cats scenario in the basic game then you need to concentrate on the Endangered Species and the Animal Enrichment option, the first to be able to purchase some of the rarer big cats, the second so that you can have that nice cat climbing tree which leopards so love.
The other advantage of Research and Conservation is that it is not an unlimited cost: sooner or later all the programmes you want will be successfully concluded, and then you can cut the funding to zero.
Some animals (such as a few of the big cats) seem determined to be unhappy, even when the specialist tells you that the enclosure you have created for it is suitable. One thing worth trying in a bid to beat this deadlock is to keep adding its favourite vegetation (watch out for the green smiley icon) until it gets fed up (watch out for the red smiley icon). Although the specialist may then tell you that the animal will be unhappy with so much, I have found that actually the happiness level of the animal(s) seems to remain quite reasonable, at least when compared with its previous miserable level. Watch this space.
Something I have noticed over the course of playing several freeform games is that it is easy fairly early on in the game to get a high rating of over 90 in the areas of visitor satisfaction, animal happiness and zoo rating, only for the ratings to start slipping over time as more and more exhibits are added, which one might think would increase guest happiness. The answer seems to be that larger zoos make for hungrier, thirstier and more weary guests, not to mention those wanting the toilet, and if their needs are not being met then your guest ratings at least will start slipping to an obstinate high 60s or low 70s.