So far people have given a lot of good advice but I can add a few tips. For the destroyer a flat area with some solid platforms above should help the purpose of the platforms is to block the bosses lasers. As for offense, you want weapons that pierce Nimbus rod is excellent as it lets you insure damage (even if you aren't a mage) but other weapons can be quite useful. For melee Dow of Pow, or a high tier spear would do quite well. For ranged get a good repeater w/ jester arrows or a gun (Gatligator, CAR, Uzi or Phoenix Blaster) with crystal bullets. in addition to the nimbus rod a mage loves to use the Golden shower on this boss. Lastly don't leave the probes around unlike before when they always gave health you will likely loose more health leaving them bee than killing them.
The next boss would depend of preference personally I take Skeletron prime out next as his patterns are simpler to handle but you might be a twins person (though unless you are a masochist don't melee the twins trust me...)