The most important thing in heads up play is to find out real quickly what type of opponent you are dealing with. So the first stage of the game must be the gathering of information. This means that you can make a call with nothing in hand after river just to see what he was playing with.
Every player follows some kind of pattern, of course in real life it's much easier to know what the other player has, because there are so much more tells. With online poker the poker tells become less obvious which of course means that they also become much more important.
I will give you some of the easiest online poker tells, that mostly apply to every player in poker. First of all, it's the size of the bet. That is the most important poker tell in online poker. People think that they have a very different way of betting hands pre-flop or post-flop, yet they deceive themselves. Only the best can consciously change their game style so completely that they leave you wondering.
I advise you - spend some time playing heads up with a guy and just watch his bet size. After a while, it will become clear what types of hands he raises pre-flop and to what amount of chips. Most people raise three times the big blinds with any playable hand, yet sometimes they raise four big blinds. Why do they do that? What happened? Now usually they've got a hand that is not so playable, like, AK or AQ or QQ. The decision to raise slightly higher amount of chips than usual, is made subconsciously for most people.
The same goes for post-flop play. Observe how your opponent plays hands post-flop. Some people will slow-play good hands, some on the other side will bet it out with big bets. The more you play with one opponent the easier it will be to tell exactly what type of hand he is playing with.
If you are playing with an aggressive player, just allow him to bet your winner hand - don't scare him off with huge bets. If you are playing with a calling station who just likes to call every bet with second best pair and no kicker value whatsoever, continue betting, but observe how much he is willing to call, don't scare him off. If you are playing versus passive player, just bet. If he has nothing, he will fold, if he has something, he will call or raise. Just don't get too aggressive, because if he chooses to play a hand, it will probably be quite good.
What is more important - head up games will definitely raise your poker read skills, which later on you will have less problems of applying in games with more people.
Heads up poker is much less dependent on luck, because basically to win in poker heads up game, you have to gather information about player and use it against him. Of course there will be times when unlucky river cards will come up, but the more good decisions you make, the more you will win.
If you are unsure of yourself in heads up play, I would suggest Sit and Go heads ups. At least with them you know exactly how much money to invest in one game, but on the other side you will have less time of discovering your opponents play, because blinds are rising up and chips are finite amount. But I would still suggest giving it a go.