Tap on your 'Social' menu and start visiting neighbors when you are out of energy but close to leveling up. Doing this will earn you XP points to level up and if you have a lot of neighbors your energy meter will be replenished as a reward.
Neighbors
You can earn coins and XP stars by visiting your neighbors and helping them out daily. The coins and XP stars you earned can then be used to purchase more buildings and level up faster which will unlock more items for you to purchase.
Placing Buildings
Before you purchase a building check to see how big it is as you may need to expand before you can place another building.
Roads
When you have removed all of the trees make sure buildings are attached to a road otherwise they will not function.