When in doubt, check the wiki!
A few tips that can make things a bit more interesting (but hardly all inclusive!)
- Summoning class staves can be used by any class with no real drawbacks. Any character even with NO summoning class boosters can have 1 free summon at any time, and they last indefinitely. Even if you only have one, pass the item around between you and your brother for free bonus damage minions!
- You can make multiple worlds and use any character you like on them. Use this to find extras of rare accessories like the Anklet of the Wind or Shiny Red Balloon, so that you and your brother can both have copies. Its also a good way to find missing pieces for accessory upgrades, such as the aforementioned Anklet of the Wind, which is used to make Lightning Boots/Frostspark Boots later on! And of course, its a way to access the Corruption/Crimson, since only one will spawn in a world!
- Pits of Honey, Campfires, and Heart Lanterns (crafted with spare heart crystals and chains) are phenomenally useful items. The latter two grant an area of effect which heals the player faster as long as you are within a screen or two, and dunking yourself in honey grants a temporary bonus healing buff as well. Excellent additions to put near your house for invasions, in your boss arena, or at a new boss you are struggling to fight.
- Use the Well Fed debuff. 'Nuff said!