I have a GTX 1060 6GB and I have played with overclocking a ton, and let me save you some time, cause it's not worth it.
The amount of performance I can eek out vs stock is so low that it really ins't worth it. If you are still wanting to overclock though, this is my advice.
1. Overclock the vram as high as it can go, once you see artifiacting, lower by about 50-100mhz
2. Bump up the core clock by 50mhz+ and that's it. Extra effort doesn't really provide better performance.
Just to tell you how "useless" the overclock is, I generally play games 50% of the time on stock and don't notice a difference.