During the exploration segments, it's important to search every location for valuable XP, health and ammo, in addition to items that reveal new story details. Don't hesitate to flip open dumpsters, go through file cabinets, investigate corpses and check computers.
Items are easy to spot, more or less. Look for ammo boxes and highlighted booklets strategically placed on top of desks or along the floor.
Keep an eye on your health, and use syringes whenever it's low.
Melee segments can be tricky. The idea is to dodge the zombie by pressing the left or right arrows just as it's about to strike, then do the same with the button along the bottom of the screen to give the creature a good push. From there, it's all about swiping downwards to nail that sucker with your melee weapon, be it a crowbar, shovel or ninja sword. The more methodical your approach, the more successful you'll be. Rapid swipes will most certainly get you killed, so repeat the process until the zombie's dead for good.
Play Challenge Mode to earn XP from completed objectives, which include surviving for 30 seconds and melee killing an enemy, among other tasks.
To switch weapons and equipment, pause the game, then select the desired tabs.
You can and should upgrade weapons/armor while inside the shop.
You can customize the controls by pausing the game and then selecting the gear icons on the right. From here, you can toggle on/off casual mode, tap to move, auto fire, virtual joysticks and other options. The more comfortable the game feels, the easier it'll be to survive.
You may need a specific item to solve a puzzle. Examples: a fire extinguisher to put out the fire impeding your progress, or a key code to unlock a door. These things are usually a room or two away.