Let's do some math here:
- Average Rush Distance: 50 seconds
- Drone Build Time: 17 Seconds
- Minerals gathered per second: 1*Drones
- Starting Drones: 6 (+50 Min)
So if he rushing you with his initial 6 this means you should have enough to build at least 2 more drones by the time he arrives. This would leave you with 8 drones to his 6. If he waits for his 7th, then you should be looking at 9-10 Drones vs his 7.
The key point here is: You should always have more Drones!
Now in 2v2 I can see how this would be an issue... if your ally doesn't help you, but in 1v1 you should always have a leg up on anyone Drone rushing.
Now many where you're falling down is Drone Micro. The key to good Drone micro is two things
- Try to surround his Drones
- If you right-click on Minerals (harvest), your Drones gain unit walking
If you're ever in a situation where he has a surround and you don't, just click minerals. This will remove his surround. Don't let your Drones get caught behind each other as you want to get a good surround. Finally, if he's dancing in and out, just mine more minerals and build more Drones. He's not harvesting and you are, and that means you can gain an even larger advantage.