Good against Protoss and Terran
- Pool at 4 supply (without making a drone). You can cancel a drone if you already made one, you won't need that larva
4/9 scout exactly at 128 minerals (when you have 120 minerals and the drone is bringing 8 more)
zerglings after that
make an extractor at 9/9 and 100 minerals, make a pair of lings and cancel the extractor (called extractor trick)
This build is viable even at the highest level. It's a hard counter to proxy 8 barracks. Sometimes you'll need to play a macro game after this, especially if the Protoss knows to abandon the forge and pylon and cannon inside the base.
Can be good against every race
- 5/9 pool
6/9 scout with the last drone you make
zerglings from now on 9/9 extractor and a pair of zerglings, cancel extractor (this is called extractor trick)
if the opponent is Zerg, make a sunken in his base, but don't make it too obvious or too early
More economy oriented build, the only hard counter to 12 hatch in base. If you do it against Protoss with the intention to macro behind it, you can make a drone instead of a 4th pair of lings.
With these two builds, I was able to get around 1800 MMR, mostly losing to Zerg 9 pools. Of course, a new player wouldn't be able to macro out of a failed 4 pool, so a new player would have a lower MMR doing this build. But a new player still gains a lot by doing these builds - learning how to scout, micro, multi-task, follow a build. I will follow up with a more interesting build for the second part of the guide.