In Day[9] Daily #345, Day[9] suggests a process for improving mechanics: prioritize it at the top of the mental checklist at the expense of other things, see what it earns you, and slowly assimilate it into regular play. For Zerg, here are a few things I can think of that might work:

• Creep spread
• Overlord spread
• Larva inject (as discussed in the Daily)
• Expanding every 5 minutes
• Never supply blocked
• Army always split into 2 control groups
• Constantly scouting
• Keeping minerals below 400 at all times
• Paying attention to alerts