When should I fight Queen Bee?
It's recommended to have at least 300 Health before you try to beat Queen Bee.
What should I have before Skeletron?
Crimson Armor should be acquired as the player should have killed their evil boss, but armor for the player's weapon class is always an option. Fossil Armor(Desktop, Console and Mobile versions) is the only armor set available for rangers before the dungeon. Necro Armor, since skeletons drop bones.
When should you fight Skeletron?
Although you can fight him at any time, it's best to wait until you have at least Meteor Armor, or even Molten Armor. We also strongly suggest you use a ranged weapon to deal with him, such as the Minishark, or a spell like the Demon Scythe. The fight itself shouldn't be tough so long as you prepared the battle arena.
Should you fight Skeletron or Eater of Worlds first?
EoW is definitely easier - though unless you're on expert mode (in which case, definitely EoW 1st) you can handle either of them pretty ridiculously early on as long as you're good at dodging.