Help me fix a cognitive bug

I have this cognitive bug, and the best way to describe it is that I am bad at macro (for anyone who plays StarCraft). Basically, whenever the optimal strategy is to do a lot of one thing, or to create a base of production, I fail to notice. (To demonstrate how bad this is, I at one point participated in a stock-market simulation and bought one of a bunch of different stocks...using up less than 5% of my total capital.)

So my question to you guys is, any ideas on how I can fix this? What habits can I drill into myself to get better at macro-ing?