Are we talking normal or expert, here? It generally helps to include such info.
Most bosses in Normal can be cheesed fairly easily to the point it is nearly impossible to die to them. Just in case you're talking about Normal...
WoF: Build a long flat bridge, and try to find a Hellwing Bow. Use Normal Arrows to take advantage of the bow's special properties. Alternatively, you can use Meteor Shot with a Phoenix Blaster (which is much easier to get).
Hardmode: The following Suggestions are all assuming you're using Melee/Tank armor.
Twins: Like all three Mechs, the Daedalus Stormbow makes the fight easy as pie; make a platform arena on the surface somewhere and laugh at the puny mechs as they die in 90 seconds or less, assuming you use Holy Arrows. If you are having trouble surviving against the biome mimics (weave around terrain and use a yo-yo), then an Amarok will do just fine. Failing that, you could also try the Megashark with Ichor Bullets if you happen to have Crimson. The big thing to remember about the Twins is that you should never, ever, ever enrage both eyes simultaneously. I would focus on the laser eye first and then kill it. If the green flame eye is the only one left, its enrage form is far easier, as all you need to do is stay far enough away that the flame can't hit you. With the other eye dead, you should not take any damage whatsoever in this phase.
Destroyer: If you have Crimson, the Bladetongue will kill him in
0 seconds before he can even take off half of your life if you position yourself right, though it might be a bit of fishing to get one. The Fetid Baghnakhs can do similar, but that requires killing a Crimson Mimic. Barring that, you can get a Nimbus Rod and rip the thing to shreds, but I've had mixed luck trying to get one. If you do happen to get one, however, it also works great on the Golem.
Lunatic Cultist: To avoid calling out Wyrms by hitting the false images, pay attention. When he splits up into 4, stop attacking immediately. You have several seconds to make a decision as to which one to attack. Three of them are darker than the remaining one. Hit the one that's not dark and the other 3 will disappear and no Wyrm will spawn. If you do accidentally spawn a Wyrm, a Terra Blade will make short work of it; usually within 3 seconds or less. The Eye of Cthulhu is usually the weapon of choice until you get a Solar Eruption. Also, if you haven't already, get a UFO mount. It makes Cultist and Moon Lord far, far easier.