Use Non-Unlocked Cars
Whatever car you have, it'll only work for the car right after the one you already have. For example, when using the black car, you swipe down to the general and press select very quickly afterwards. When you unlock general, you do the same to use the next car, etc.
Use cars you don't have
Find a car you do have. Then scroll down really fast to the one you don't have and click select.
Related: Zombie Highway Gameplay Trailer
Shooting: Hold vs. Tap
Keep in mind guns have different firing rates for holding vs. tapping. Handguns specifically can fire much faster when you TAP. Tapping quickly can be more distracting than simply holding, which is why you are rewarded with a greater fire rate.
When a zombie’s life bar blinks, you will do double damage. For weapons like the double barrel shotgun, this means serious damage.
Avoid Getting Flipped
If the zombies get you on two wheels turn into the roll to recover. This is simply physics working in your favor. If you are up on your right two wheels – sharply turn to the right. This will snap you back on all 4 wheels if you do it right.
Minigun for free
You have to drive 500 miles to get the minigun.