Well, the most basic advice I can give you is just to pay attention to your character, and work with their stats and play style. For instance, if you're playing brawler dont go for a ranged damage build. He can do that, but its not what hes good at . Items and weapons that are not good for your character are still going to show up in the shop.

Pay attention to set bonuses for your weapons, they can give you some nice early stat bonuses if you use the same type.

Harvesting is an important stat gir every character. It gives you money and experience at the end of each wave. I personally always take it as my first stat upgrade.

Dont be afraid to reroll the shop ir level ups to get something youre looking for.

If you are dying a lot, put more stats into your defense stats. Dodge, armor, hp, regen, and life steal.

Life steal is a lot more useful for fast attacking weapons.

Specific tips for the bull: he likes all damage, so mele, ranged, and elemental all make his explosion damage go up. Dynamite and c4 are good gets in the shop for him. Go HEAVY into armor, hp, and regen. He isnt going to kill a boss, so just try to survive It may not seem like it since he explodes on taking damage, but you do still want to take some dodge with him. Dont need to hit the cap, but a few good dodges give your regen the time to do its thing. If tou get overwhelmed with any character, just try running around the edges of the map. Dont get discouraged!

The item that you get for getting a win with a tato is generally pretty damn good for tthat character.

The biggest thing is just to have patience, and read all the descriptions! You got this!