Watch some of the day[9] dailies at http://day9tv.blip.tv and you'll improve at least a little bit. Watch the episode on the Mental Checklist (http://day9tv.blip.tv/file/3732340/) first.
Since I started watching Day[9], I've figured out why I'm losing to Gold level players.
Reactive Zerg tries to balance power-droning (making nothing but drones) with reacting to the opponent's offensive postures. Ideally, reactive Zerg should only produce military units right before an attack, and only produce those units necessary to fend off the attack without taking other damage to its economy. Reactive zerg wins mid-game or late-game after their economy blows past that of the opponent.
I'm still in low Silver because I'm trying too hard to play reactive Zerg now... however, it's teaching me to keep growing my economy after the early mid-game. Once I switch back to a somewhat more offensive Zerg, I think I'll have an advantage that I didn't have before.