Zerg Droning

Hey all,

Was watching some ASL and Tastosis were talking about how with toss and terran you can constantly make workers whereas with zerg its much more complicated. I've been noticing that as zerg I constantly lose games by being super greedy (it's a SC2 zerg habit I think). So basically I have no idea when I should be making drones, when I should be making units, when to make new hatches. Also probably related is when I should be making sunkens/spores. Any general guidelines about this?

What often happens to me is that I scout an attack halfway across the map immediately after I've morphed 15 larva to drones, and I feel completely helpless. For a beginner as toss or terran it is more obvious, because you simply always produce out of your gateways/rax/facts, and the important question is when to add on new production or CC/nexii. But I really have no idea how I should manage zerg production in BW.

As a side note I do like to play a macro style, so I'm not really interested in attacking in the early/mid game any more than some light harass (or not at all considering my skill level). I just need to be more on top of my defense.