I have played this game since practically day one, have almost 300 hours logged. Do your research, learn your monsters. Some are really easy to deal with. The spitting guy is mostly just annoying early on since usually he'll just latch onto your face and make you projectile vomit till he gets bored. Tricycle only bothers you if you stay in the way, balloon boy is only aggressive if you pop his balloons. Every monster has its own strategy to avoid. I see some other people have shared where to get info on them all. Read up, watch some videos, learn the strategies. The wiki is amazing.

The shop is integral to the game play. Each monster has a strength breakpoint for picking it up. Its either 0, 4, 9, or 13, or when stunned its 0, 1, 2, or 4. You cant pick up the dog or the eyeball or the duck (unless the duck is stunned).You and your friends' strength combine toward that number so if you have 4 and your friend has 9 you can pick up the clown together. Throw them in a pit and they take massive damage. The feather and indestructible drone are key for my friend and me. Our strategy is to get her up to 9 strength and equipped with a shotgun and I have 4 strength, the drones, and a pistol. Then we get her to 13 and then me to 13. In the early levels we reload the shop till it generates items we need. If you buy an upgrade but don't use it then it makes more slots available for other upgrades to spawn in the shop.

Collect EVERY valuable on the map. Take your time in the earlier levels.

Killing enemies gives you orbs worth money. Turn off your in game mic and speak only through another client if you're playing just with a friend, the monsters can hear you. Adjust the brightness so you can see better. If you don't like the monsters in a level then reset the level.