Combos
Serve the bigger planes after the small planes if possible to get a larger combo bonus. Also, bigger planes are more impatient.
Try purchasing a repainting plot so you can make all your gateways reach a 4x combo of each color. This is the maximum, and you will get the most combo points and a medal at the end.
Hidden cinematics
Each airport location has a "hot spot" that you can click on for cinematics, dialog, and other hidden features. For example, click the church at Happy Valley Municipal.
Medals
Give planes with an emergency, such as "organs transplant" or "baby delivering immediately" priority, as they will get very impatient, and you will be awarded a medal.
Combos...