i dont typically have a certain range. it always depends on who else is in the pot and what they've done. if the BU opens to 3x and i know this person is a typical tight aggressive player, steals a lot in position (thus has a weak range when he opens 3x on my BB) i'm going to be 3bet bluffing him a lot. because he folds heaps. if there are two limpers and then a very aggressive player (who likes to raise preflop and doesn't fold to 3bets very much) raises in the CO, i'm going to decide to 3bet a lot of hands for value from the BB that i wouldnt against other players, like maybe 99+,A9s+,ATo+. dont take it from me though. i suggest you search and work through spoonitnow's beginners circle exercises which help you understand exploitation and adjustment (i think the threads are called "Spoony Exercise 1: (topic being covered in that post", "Spoony Exercise 2: (topic being convered in that post)" etc). once you understand these posts, i'd search "Blind stealing 101", "blind stealing 201" and "raising behind limpers" to get a more in depth look at preflop exploitative play.