Hello there, As we all know, multitasking ability is very, if not most, important thing in Starcraft 2 (in other RTSs as well). But how to develop this ability? Great solution that is working for me is mini game called Multitask 2. It’s pretty straight forward: you have to play up to 6 very simple mini games simultaneously and the longer you play, the harder these games becomes. Beside improving your multitasking it also looks really well. The game might look easy when you look at it, but you will change your opinion when you try it yourself. I recommend watching short video I made playing Multitask 2 myself: http://www.youtube.com/watch?v=GW-1Oq6U9HU Gl and have fun training!
How about just playing a lot vs people? because you should always be multitasking. that game doesn't cover all the kinds of multitasking a player must do in a normal game.