Always check back for a daily reward.
Always expand your land even though it costs. Good thing is you have the option of spending gold coins or Airport Cash on it.
You won't gain access to new buildings, planes and destinations without leveling up. Go completing missions regularly and flying/landing planes, as doing both results in a little XP.
You can always view the current inventory by clicking the Warehouse (wooden box) tab at the bottom of the screen.
To sell buildings and objects press the arrow icon at the bottom of the screen, selecting the piggy bank and then tapping the item you wish to sell.
The bigger your town/airport gets, the more electricity you'll need so you'll have to invest in some Power Plants to generate more electricity.
Keep in mind that each plane needs its own hangar and that costs.
The more runways you have, the more planes can take off and land at any given time and you get more $$$.
Upgrading the Town Hall increases a city's population, while upgrading a terminal lets you house more travelers.
Fuel Stations will be able to keep the fuel pumping to you with your minimal effort.
If you receive requests from pilots to land at your airport let them. Letting them do this will cost you a fuel, but you'll gain gold coins and valuable experience points.