Before we begin, let me try to settle once and for all why achieving the most accurate and neutral sound should be the golden standard that all music lovers, audiophiles, and audio professionals, and why intentional coloration is not a good thing for most people. Whatever slight subjective coloration among them all fall within that acceptable range of accuracy/neutrality.
This is the golden standard used by the professional audio industry and everything you've ever listened to that's produced by professional musicians, producers, mixers, mastering engineers, etc., adhere to that golden standard. I want to state at the beginning that experienced, informed, educated professional audio and advanced audiophiles understand that the most ideal sound is within that small range of acceptable accuracy/neutrality in sonic signature. The other tutorials usually tell people to use pink noise and sinewave generator, and while those are useful tools, they are not the easiest or most reliable for people who are inexperience in critical audio assessment at the professional level.
There are other tutorials on how to EQ headphones, but I haven't seen one that teaches people how to do it in the most reliable and easiest way possible. I've been wanting to write a comprehensive guide on how to do surgical EQ corrections to achieve the best sound possible, in a way that is the easiest and most reliable, without any guesswork and constantly wondering if you got it right.
(UPDATED on April 16th, 2020, with new links to missing test tones and YouTube videos.)