I have two builds that I switch between. The first is getting gas at 15, expanding, and get upgrades behind MMM. The gas allows for the upgrades so usually when I'm ready to engage, stim and combat shield are finished along with +1 attack. This usually allows me to win the first engagement and push straight into the base. It is also more flexible.
My second build starts the same with 15 gas with an expansion but I build 1 racks with reaper. When the reaper finishes, I use it to scout only around my base for proxies since I need it. I drop a reactor as soon as the reaper is out and build a factory. I swap the factory and racks, then build a 2nd factory. The only thing from the factories will be cyclones. I start +1 mech weapons when the armory finishes. This build is more dangerous since it relies on speed and is punished by proxies and rushes since the reaper is the only defense. If a proxy is scouted, I switch to MMM until I can mech up.
I haven't experimented much with these builds. I mostly rely on them working and do little to vary the build. I just go for overwhelming numbers.
For good builds, check out PiG's YouTube/stream. He is a modern Day9 with his videos. Hope this helps.
I highly suggest you check out spawning tool! It is a fantastic website for all sorts of builds! My suggestion is to find a build, one versus every race, and practice them till you master them and then move onto other builds. If you pick the builds that are posted by PiG there will be an instructional video that goes along with it! Spawning Tool: LotV Zerg Build Orders