for better micro i suggest...
1) Make good use of the Alt key.
Run low hp units back, if your opponent decides to chase you get free attacks on them.
2) Learn advantages/disadvantages of armor/attack types.
Kill the easiest things first
3)If you have casters, USE THEM!
I've seen many replays of people w/ master sorcs and they just sit there and cast slow, same w/ witch docs, if you have them, use them.