Microing

Last-hitting earns you nice shiny gold
Microing

Your Hero is not immortal. Your Hero is weak-sauce. You should be a chicken!! This is especially when your hero is at low levels. What you want is to make sure that your Hero takes little or no damage if possible, but yet constantly levels up. You gain experience as long as you are in 1000 range of any enemy unit that dies. But if you die, you have to wait a period of time before you re-spawn again. This sucks and staring at the grime on your keyboard sucks too. So do try to avoid dying.

What you do want to do is stay behind a little bit from the battle going on. And only go in every once a while to land a last hit which kills an enemy creep to get gold. Once you feel comfortable with this, try to deny by killing your own units which are about to die to stop the enemy from getting gold and experience. Hold on to the Alt-key and scan for anything with a small bit of red-health left and go kill that unit. A small amount of experience (18exp) is given for each deny as well.