I was in the same boat as you. It takes a lot of practice. If you don't mind downloading more software, Royal Vegas
Poker offers Head's Up SNG's at lower prices, As low as $1 I believe. They also give you $10 to try out the software, so there's 10 games to practice.
In heads up you generally need to be aggressive AND patient. Be aggressive a lot so the person has a hard time putting you on hands, and when you get a monster hand, hopefully they'll have an ok hand YOU can trick THEM into putting you all-in, and then you win. So aggressiveness plus patience equals winning heads up!