Play with others
stressing this point harder: if you intend to just solo your way through everything, bosses and some missions will range from "really hard" to "hellish" even with decent gear. play with a friend (or a random guy off region chat) and the range will go down to "pretty challenging" or even "cakewalk", depending on said friend's loadout.
also:
die in multiplayer? your friend(s) will get a window of time (~15sec) to revive you back to full health.
die solo? GAME OVER YEAAHHH (unless you want to waste revives, which is generally a bad idea)
basically don't play solo, unless A) you're sure you can take it or B) you have a death wish.