Undead Soccer is one of the millions of Zombie games on the iOS platform, but unlike most of the rest of them, this one actually happens to be fairly unique in premise and in execution. Your goal is simply to swipe to kick soccer balls at zombies before they kill you. They come in waves, a la Space Invaders, and the further you go through the waves, the harder that the game becomes, so some tips and tricks surely become helpful at some point.
When you hit wave 4, you will end up fighting a boss that at first seems almost impossible to beat. However, one of the easiest ways to beat him is to do the following trick. You can curve the soccer ball after you shoot it and before it hits the zombie. Swipe up to shoot the ball and then swipe sideways while the ball is in mid shot, and it will curve. You can even curve it in multiple directions if you want, one after the other. Curved shots will hit the first boss without your shot getting blocked. This also works for the shield zombies and others who are tough to kill.
When the bomb zombies come onto the screen, wait to kick a ball at them until they have other zombies around them. When you do this, their explosions will kill the other zombies. When the other bomb zombies get hit by the explosion, they will explode too, giving you the potential to create a daisy chain of explosions, killing lots of zombies with one shot.
If you want to get far in the game, the most important power ups to get are the ones which upgrade you at all times, especially the one which shortens the amount of time that you have to wait before you can kick again, or the one that increases the power of your kick. Upgrade the kick time one, especially, multiple times, and save all of your coins for it. The faster that you can kick, the better that you will do in the game.