Occasionally try talking to everyone in town. Pauliver will give cards after certain conditions have been met, and the Librarian will give you hints on unlocking new cards.
Clearing all of the enemies on a floor grants a bonus to experience.
You do not need to fully clear every floor! Sometimes it's better to move on than take unnecessary damage.
If you're only missing one or two enemies, they may be Dino Slimes hiding. They tend to lurk near items on the ground.
Cursed items cannot be unequipped, but can still be worth using, especially high tier items.
Scholar is an incredibly strong chaos card that allows players to have essentially twice as many orbs per character level, with the only drawback being a smaller selection.
Rapier + Sliding Boots - Insane mobility and unlocks a gear card to start with these items.
Blade Barrier Spellbook + Siphoning Orb / Mana stone - Blade barrier is incredibly strong, allowing you to dive into hordes of enemies without fear. Siphoning and Mana Stone will replenish your charges.
Raise Dead Spellbook + Siphoning Orb + Pet Armor / Friendship Flag - Raise dead can create huge numbers of pets for the player, more of a supporting combination.
Scholar chaos card + Orb Pendant - The Orb pendant will create an extra (free!) orb every floor, which gives you more options if there are no good orbs in the shop.
Rapier + Auxiliary Attack Orb + Shocking Feedback - Increases spread of rapier and gives additional room clear for the rare instances you get hit. Shiny Mirror is a good complement, since most spells are harder to dodge than the vast majority of other enemy attacks.
Wizard card + Insanity card + Ace card + Siphoning - Still difficult because you only have 1 life, but very fun. At 1 life Ace will auto spawn on every floor, and his attacks will trigger siphoning. That combined with the mana regen of Insanity will keep Dimitri's Chaos charged up.