On the Zerg however, especially when I'm under pressure, I tend to keep building units instead of drones to fend off the enemy, and before I know it, I'm out resourced. By mid-game Protoss would completely smash my army with their immortals/zealot/stalker.
Sometimes I would build too many drones with too much minerals and not enough gas to spend the minerals with. Then comes the army and I get smashed.
Any tips would be great!