Entry location: Any time you fight a boss
I know that there are already tons of tips on how to kill bosses, but after reading them I discovered that most of them involve taking a katana or small chainsaw and simply cutting them up. I have some tips for if you simply don't have the health to do that.
Cletus, In the Huntin' Shack (North Plaza)
Alright first of all simply run out of the store. Now you should kill all the zombies out there to give you some breathing room. Once that is done, open the door to your left (Cletuse's right) so that it is opened into the store. Then simply stand at the edge of the wall to the left of the door and aim with your gun. Due to Frank's natural right lean, you will be able to shoot Cletus while safely behind the door. If you run out of ammo, there is a corridor to the right on your way back to the North Plaza that usually has 3-4 zombie cops with guns.
Carlito (Food Court)
This fight is pretty easy, although I still wonder why I cant get his gun. Run up the stairs roughly in front of you so you are kinda under Carlito. You should see a stack of boxes to the right, jump on then, and then onto the same level that Carlito is on. Basically use the same tactic you used on Cletus, go to the edge of the wall, aim, and shoot. (Note: The handgun has a rather small range, so If you're shooting right at Carlito and hes not taking any damage, just wait until he gets closer.) After a bit of this, he will run away to another section of the roof. For this I reccomend jumping down next to Brad and Shooting Carlito when he comes out from behind the sign. Because of the horrible AI, Carlito will always run out to the same spot, so just aim right there and hit him when he stops. If you run out of ammo, just talk to brad and he'll give you another gun.
If you're like me, then you got pretty frusterated by these guys. All you have to do, however is raid the Huntin Shack and grab a couple shotguns and maybe a sniper rifle. (If you havent killed Cletus, then this fight is a lot harder, so I would reccomend doing that first.) If you like being up close and personal, then simply blast the convicts with the shotgun when they try to run your over. I recomend killing the gunner first, then the guy with the bat, and then the driver. If you find that you keep running out of health when you do this, then I would reccomend trying out the sniper rifle. Just run away from them until they become preoccupied with something else or get stuck behind a tree, and then kill the zombies in a rough 25 ft square area so you can aim. Then just zoom in on the convicts and take out the gunner, then passenger, driver. It is kinda touchy while aiming, so you dont need to nessecarily go for headshots, as long as you hit them. Note: If you dont destroy the car after you kill the convicts, they will simply come back next time you enter the park. I reccomend taking the gun off of the back and shooting the jeep until black smoke comes from under the hood. If you're not sure that its completely destroyed, then check if you can still get in.
Carlito when he has a sniper rifle. (Entrance Plaza)
First of all, when you use this trick Brad may become low on health, so be sure you keep an eye on him. Run up the stairs, and follow Brad to the sports store. Then you need to make a quick dash to the pillar closest to the store. If you jump in the middle, you shouldnt get hit. Use the same trick as with Cletus and Carlito the first time and hide behind it. Sadly, the sniper rifle does not work with it, so its pretty much useless, unless you want to take pot shots at Carlito from the stairs. He will be out of range most of the time from that first pillar, so I reccomend running left to the other side of the second floor, and running up until you are directly opposite of Carlito. Then use the same trick, but you should be able to hit him this time. If he starts to run towards you, then you need to retreat because he can then get a shot at you.
Steve (I dont know if thats right, but hes the leader of the raincoat cult) Movie Theater
This is pretty simple, and, despite what I said earlier I reccomend a katana. The shotgun is hard to use because he is always in your face and its pretty hard to shoot him before he stabs you. So I would just wait until he attacks you, sidestep it, and get in a quick slash or two while hes recovering. Keep this up for a bit and he will drop pretty fast. As for the cultists that come running in afterwards, that is what the shotgun was made for. Just put a couple pumps into the group, wait for one to charge you, and let him run up to you. You will then enter a grapple, and its pretty easy to win. Once you push him over step back, and, if it went right, most of the group should be over the body when it explodes. SPOILER: The book that Steve drops is called "Brainwashing for dummies" XD
Adam (Wonderland Plaza)
This is a pretty easy fight, despite how much everybody else whines about it. First of all, you need to run down the stairs to the second floor. Once he follows you, stay at a distance of about 10-15 feet away and wait until he starts to blow a balloon. (If he decides to throw a knife just dodge it and he will problably blow a balloon, and if he does the flame breath, then your too close) Shoot the balloon, and keep shooting him while he's stunned. This is pretty much the entire fight, and I got it the first time without losing a single bar of health. If he jumps down to the first floor, then DO NOT FOLLOW HIM. There are tons of zombies down there, and it is much harder to kill him. Just wait until he comes back up to the first floor.
Final Boss (Dont remember the name, but hes the guy on the tank.)
First of all, this is a very hard fight. First he will do a little "come here" gesture but ignore it. If he doesnt charge you, then bait him by running up to him and back really fast. First he will kick at you, then he will yell and charge you, usually knocking you off the tank. Sidestep that, and beat the crap out of him as soon as he passes you. Any technuiqe will do, I used normal punches most of the time. Note: When he blocks your punches he will take a tiny amount of damage, so once his health is about at one quarter left, just keep punhcing him and letting him block it, and after about 2 minutes he will die. I also found that if you are constantly falling off the tank and getting bitten several times, then scan the edge of the zombie crowd for some that have queens. I found a couple next to the wall, so look around. Kill that zombie and throw the wasp-in-a-jar at the crowd. You will kill about 200 every time, so if you do that 2 or 3 times the zombie crowd will pretty much dissapear, so you dont have to worry about falling off the tank.
Thats all I have, I know there are more bossess, but I dont want to ruin all the fun for you >=)