Positioning and map awareness is the most important aspect of the game to focus on in the beginning. Often its not about killing an enemy, but zoning them so you get better positioning than them. There are a lot of good advice in the posts above. The only advice I want to add is to pick a Hero that make it relativly easy to stay alive. I cant think of a better Hero than Raynor for training. First of all he automatically heal for a large amount when you are below 30 % health....