I almost always raise 3 times the big blind if I'm going to raise at all before the flop (there are exceptions, for example if 9 players limp in and I'm in the big blind with pocket aces) to avoid having identifiable patterns in my betting.

Concerning minimum preflop raises, what is the raise supposed to achieve? When you raise the minimum before the flop, you aren't really accomplishing anything other than playing an essentially limped pot that is twice as large. Raise more to extract the value of your hand.