I seem to be having more and more trouble in the Zerg vs Zerg matchup. I can't find a reliable, good, build order/ opening. What is an effective build order or build opening that I can use to safely progress in ZvZ?
14 gas pool is my standard build for the matchup. The timings are actually pretty easy and if you miss something and notice quickly it still works out nicely, you can just get something else faster. It allows you to get a very quick speed up almost as soon as your pool finished and lets you safely take your natural expansion.
This counters an early pool pretty well if you just micro your drones around and delay. It gives you a timing window to hit against hatch first builds where you'll have speedlings for a while before he does, and you can exploit this to pick off drones, out of place queens, etc. If they start throwing down spine crawlers you can safely drone up and home and just scout to make sure he's not hiding any tech.
If he goes Banelings, go Roaches. You'll have to micro pretty intensely for a bit if you don't scout this ahead of time. If he goes Roaches, you can either defend on pure Speedling/Spines and tech to Mutalisks or go Roaches yourself. If you tech to Mutalisks you have to take 3-4 gas and do it quickly and preferably secretively or he'll have plenty of Queens/Spores/Infestors out in time to deal with it.
Example game: here. This is only against the very hard computer, but you get the idea. He goes for an early ling attack and kills a Queen, then I just contain him on one base until I have enough Zerglings to go for the kill. My teching to lair was a bit late.
It's by no means a professional build but it's a safe way to transition into a macro based ZvZ.