Try to get the Aim bonus as often as possible while fighting the zombie. This reward you with more resources, but is difficult to get. You must stand still facing zombies and hit them when they arrive. This works best with solitary zombies, or when there is no risk of getting surrounded.
Area Clear bonus
Always get the "Area Clear" message and bonus before exiting a level. You will win a special bonus from the chest, which may be wheels, perks, coins, or premium currency.
Arena
Play in the arena as often as possible. You will earn 1 premium currency for every 80 zombies killed. This will be easy to accomplish after you are able to use a firearm.
Armor
Save gears for armor. Armor never regenerates and each shield (maximum of five) costs 150 gears. Make sure you have enough gears for one shield purchase before entering a new level.
Defense
If you have firearms, remain moving in circles and shoot the zombies. If using melee weapons, keep moving backwards in a straight line. Avoid getting trapped in corners while moving. Stay away from the zombie horde. Keep clear unless you have no other option than to face them.
Perks
You have two slots that can be used for perks. Get those that suit your play style. For example, when using pistols get the perk that helps you find more handgun ammo and combine it with the Glitch bonus. The experience point, speed increase, and increased range for picking up objects are a waste of points.
Scavenging
After getting enough premium currency, spend it to scavenge the area you are in to find items lost by other players. You can find new weapons and other helpful items. Occasionally you will see cities that are smoldering. Investigate them to gain easy resources with very few zombies. However you will not get an "Area Clear" bonus.
Weapons
Keep the crowbar for awhile. It is not worth investing in the axe. The crowbar will increase its rating while you save for better weapon, such as the revolver. After using it for awhile, save and purchase the pump shotgun.