First off, remember that attacking is the only way zombies can die. Upon dying, zombies require either a toxin or an 8-hour time-span to revive.
Upon attacking a restaurant, first examine the enemy. You'll find that there will be some waiters and waitresses as well as one chef cooking. The waiters and waitresses are easier to kill and do less damage than the head chef.
It is best not to let your zombies behind the counter. It can become cramped and often forces a 1 on 1 fight with the head chef which will most likely kill your zombie. Keep them out from the kitchen. When the head chef finally comes out, typically most the the restaurant will be cleared by then, this lets you attack the head chef with multiple zombies, killing him before he really does any damage.
If you tap a zombie and then tap a person, then that zombie will hone in and exclusively attack that one person. If you press the attack button, the zombie will simply enter the restaurant and attack randomly.
Zombies (and the defenders!) fight by first acquiring a target and then attacking that target until 3 things occur.
1. The zombie or the chef dies. After this, if the chef won, then it will proceed to target another zombie. If the zombie won, then it will bend down, consume the body for some (typically minimal) energy, and the move onto the next target.
2. You command the zombie to retarget by first tapping the zombie and then the target.
3. You retreat.
Only the waiters, waitresses, and chefs actively attack your zombies. The customers just run around screaming.
Eaten customers and people restore energy relative to their own fighting prowess.
Ex. Eating a foreman (a powerful fighter) will restore more energy than eating a retiree (weak fighter)
Upon being attacked, zombies and defenders automatically retarget to the attacker. This ends up making any attempt at running away without using the retreat button difficult.
The AI works in descending order of importance as below:
Retreating > Being attacked > active command
Food acquired from attacking is completely random. You may acquire foods that are many levels ahead of you.
Attacking is the only way to acquire dish variations like 'spicy' or 'quick' (unless a friend makes a dish you don't know and gifts it to you).
You may steal the food before beating the chef. Simply click a zombie and click the food. The zombie will then walk and steal the food. After that, you can continue fighting or retreat. But note that stealing food will take a few seconds so be-aware of enemies approaching.
When fighting a higher level cafe, to reduce the occurrence of your zombies dying, take out one target at a time (i.e. kill a waiter, then retreat). It's a lot faster to heal your zombies than to wait for the 8h revive + heal. But this technique has some flaws, your zombies might be "ganged-up" so please take precaution.
Time the zombie activation. It's best to have the zombies enter the enemy cafe at approximately the same time in order to avoid having a zombie engage the enemy waiters by itself while the others are still walking in. Start the slow zombies first, and then the faster zombies a little later. The zombies at the bottom of the game will need to also walk a longer distance compared to the ones on the top.
Wait for the enemy cafe to be empty so that your zombies don't get distracted and attack the customers. The waiters and enemy chef are the primary targets.