When HU, calling from the SB is not an option. It conveys weakness. The aware player in the BB will always raise you if you merely call from the SB. It's like letting you see a flop for free. Unless it's just a "friendly" game, you MUST raise from the SB or fold. It's that simple. I'm still working on that myself, but I'd rather fold my SB than just call because calling gives the player in the BB too much information about my hand (ie I want to catch a good flop). He doesn't want you to catch a flop so if he raises you out of the hand PF he gets your chips anyway and doesn't risk you hitting a monster. Plus post-flop play is very important HU. You must always put your opponent on his heels with each bet. Then when he comes over the top of you, you can lay your hand down knowing you're beat. Up the aggression, play with confidence and you'll turn your HU game around.