When you are in any zoo mode (campaign, challenge, and freeform) most zoos should have already existing trees(and occasionally things like flower beds, benches, etc.) at the start. All you have to do is left click the item you want and move it to where you want it.This saves money when you are on a tight budget and is really easy.
Run in Zoo Guest Mode and Photo Safari Mode: Since left-clicking the mouse makes you walk in Zoo Guest and Photo Safari Mode, and so does W or Up, you can walk twice as fast (aka run) by holding two of these.
While in Zoo Guest mode, hold [Cursor Forward] + Left Mouse Button to walk faster (run).
Alternately, press [Up] + W in Zoo Guest mode.
To run even faster in Zoo Guest or Zookeeper mode, hold [Shift] + [Forward] (or W) + Left Mouse Button.
More starting money in challenge mode:
In challenge mode, put the pointer over the "Up" button hat increases your money, but do not click on it. Press the [Up] key on the keyboard to increase your money twice as fast.
Put a fence around the entrance to the zoo so that the entire zoo qualifies as a cage.
Then, cover the whole zoo in savana grass and add plants and lakes. Place some animals then walk around as a zoo keeper/guest. To do this faster, do not get staff, food/water dishes or shelters. It will look unnatural. If you put gazelles in a pack, only put about two to six of them or some might ditch the pack. If you encounter across a dirty animal, wash it or all the animals will get sick and die. Note: Plant eaters will get eaten.
Make a small pen. Put meat eating animals in it and put a vulnerable herbivore in it. Eventually a carnivore will kill it and the herbivore will become a carcass of meat.
You do not need two animals to have a baby. Just adopt a female animal and wait for about a month. Then, adopt a male of the same species and place him in with the female. Do not do anything from the time that you adopt him until the female gets pregnant. When she does, select "Undo". That will undo the adoption of the male and your female will still be pregnant.
Complete five game challenges.
Complete five photo safari challenges.
Mysterious Panda campaign:
Complete all scenarios in the Conservation Programs campaign.
Complete all scenarios in the Troubled Zoos campaign.
Complete all scenarios in the Zookeeper In Training campaign.
Gilded Panda statue:
Complete all scenarios in The Mysterious Panda campaign.
Complete all scenarios in The Globe campaign.
Complete all scenarios in the Prevent Animal Abuse campaign.
Make water deeper:
Choose the "Deep Water" tool, and use it as you normally would. Then, select the "Ditch" tool and use in the deep water you just created.