Attacking
Try to use a character that has a ranged attack. Melee attacks usually will get you hit back in return. Ranged characters can attack a target while moving. Consider playing as Katie Kantmiss when starting the game. She has long rang arrows, allowing you to remain safe while attacking. Her special move can eliminate larger groups of enemies. Alex Awesome also has a short range laser ranged attack.
Police car
Complete the mission that requires you to break the police barricades with Officer Kuffowitz's car. His car can be found parked towards the east of the plaza he is standing at. Tap it and you will be able to drive it for 20 seconds. Run over as many objects or enemies as possible to get easy money, blocks, and experience.
Special move
Each hero has a unique special move that can be activated through a special tap or swipe. Such moves usually hit hard and can often take out an enemy with one hit. Once executed, you must wait until they recharge before using them again.