Loot Crates
Approach loot crates with caution as zombies have been known to hide behind them waiting to catch you off guard.
Maintain Weapons
It is important that you keep on top of maintaining your weapons. Make sure you do this whenever you find weapon parts which are necessary to either build a given weapon for the first time or to upgrade it.
Level Goals
You need to pay attention to level goals before you start a level because the more goals you complete the more Stars you will earn and the more stars means better weapon parts in the weapon lockboxes. You can always check the goals in the 'Pause' menu if you are not sure.
Perks
Don't waste perks on your first attempt at a level, it is more beneficial to equip perks when you know what you are going up against.
Replay Levels
Remember that when you replay levels you use less stamina. When you play a level for the first time it requires 3 stamina but once you have beaten that level every subsequent playthrough only costs 1 stamina.
Large Obstacles
When you are advancing through a level try to keep your distance from large obstacles that could obscure a zombie. These large obstacles include things such as hills and cornfields.
Knives
Carry a knife as this gives you one more chance if you have run out of ammunition for your weapons. You can find knives in loot bags and crates.
Daily Trials
Consider playing the Daily Trials as they don't cost stamina to play and they allow you to try out weapons you have not yet unlocked. These special challenges task you with getting specific kill counts and reward you depending on the goals you meet. Doing the Daily Trials because it is free is a good way to get practice for the regular levels.