If you need help with a particular stage you can always access the game's Facebook page by pressing the 'Help' button. On the Facebook page you will find a strategy and upgrade tips that will guide you.
Spin the Tower
Using the button at the bottom of the screen you can spin the tower by 180 degrees. This feature is invaluable for covering multiple construction routes.
Upgrading Powers
It is crucial that you spend your coins wisely when upgrading your powers if you want to make it through the campaign.