I'll raise to 4x the bb about every time I'm on the button unless I have 2 low unsuited cards. The object is not to get them to fold, but to just build the pot when you have position on them. Don't feel obligated to always continuation bet as they will be looking to check raise you a lot if you do. Raising preflop makes the pot bigger and makes it more tempting for your opponent to move all in more quickly. The game just takes way too long if you are playing a 40 chip pot before the flop in my opinion. HU is all about playing the player. Its hard to give very general advice.