When playing HU you need to mixup play and yes definitely stick to your instinct. Keep in mind that the other playing could have anything. Take special note of how your opponent is playing certain hands such as draws, top pair, mid, and bottom pair on the flop turn and river. So many factors can attribute to any decision in poker and this is especially important in HU play. Playing online is a little more difficult to get a read on a player, but noting your opponents style of play is important. Every time you get to see a hand of your opponent, that is valuable information that can be used in later hands. The more you play HU or one on one the better feel you will get. If you play on stars I suggest playing some $5 HU matches on stars or other sites if they offer them. The more hands you play heads up the better you will be come, and HU play will increase ability to read opponents as it is essential to winning in any HU match.