You need to be aggressive. Starting hand requirements go way down in HU, to the point that any hand can be called for the SB.
In fact, unless you know your opponent will raise you every time you only call, you would be folding great pot odds
by folding your SB pre-flop(you are always getting 3:1 odds in the SB) so you should (almost) always call.
Because your starting requirements have gone down, you also have a good chance to have a very well hidden hand, then ch/r if they bet into you. I love HU because it's man to man, you get a better read about that one person and not the whole table and attack their weaknesses.