There's the "official" ROG Overclocking Guide For Core i7 5960X, 5930K, and 5920K. And plenty more all over google.

Best quick advice is to focus on one component at a time, one setting at a time, going through them each methodically. Push multipliers up a small gentle increment, boot and test (run some benchmarks or games or whatever) for a while - if the system is stable then repeat, if the system is unstable then back off a notch or bump voltage up a tiny increment, etc. At some point you will have a "maximum" overclock for your particular parts, you won't be able to push any faster without cooling or power upgrades. At some point above the "maximum" overclock you will have an "ultimate" overclock threshold for your particular parts, nothing you do or upgrade can possibly push them any faster. Carefully take notes and log test results, with enough data points you will be able to graph a "sweet spot" which gives optimal results.

The R5E provides a ridiculous number of fine settings you can adjust (and that most excellent phat OC socket). Many of them, incorrectly configured, can do Bad Things to your system. Don't adjust anything unless you know exactly what it does.

I don't personally consider an overclock "stable" unless it can run 100%+ stress loading, say some Prime95 instances, uninterrupted over a full 24 hour period - without crashing, bugging, or overheating - faster is better, yes, but no amount of performance is of use to me if I can't depend on it working reliably. Many people are happy to push a little faster and further with their system "stable" enough to game for a few hours at a stretch between BSoD reboots. A few people want to break records and they only need their finicky extreme system configurations "stable" for the precious few minutes it takes to get a lucky screenshot. Exceeding manufacturer-rated specs (ie, overclocking) is never going to promise 100% stability.