My impression is that the O.P. is looking for specific skills more than things like "be mentally tough" and the like ... ?
As Christine said, one of the specific skills you need is the logistical stuff; I suggest that you "gain that skill" by just getting Yogi's guide and using that.
In a list of specific skills I would include (and prioritize) foot-related stuff, but not so much a general "expect foot pain" comment, but "know how to deal with common foot problems". Specific issues I've had on long trips included blisters (common at beginning for first time thru-hikers), morton's neuroma (pounding the nerves at the ball of the feet), bunions/bunionettes (get wide-toed shoes), extensor tendiopathy (don't tie your laces too tight), and the very common plantar fasciitis (look it up). Lots of ways for feet to go wrong; knowing some of the more common issues in advance might help you stay on trail or get back on quicker. Foot problems are one really big thing that ends trips for people.
Other than feet, just knowing "most common" first aid type of issues. What to do if you get giardia-like symptoms. What to do about cuts, gashes (often little or nothing, but knowing when nothing isn't the right answer to prevent, say, blood poisoning). Etc.
Food: how to resupply with adequate nutrition that you'll actually eat, in somewhat limited circumstances (such as a gas station mini-mart where fat/sugar content is high and food value sometimes difficult to come by).
Certainly navigation is a specific skill, which includes map & compass, plus optionally gain experience ahead of time with a GPS if you have one.
How to dig an efficient (and please, deep enough) cat hole. More generally the whole "how to defecate in the woods" thing.
If you're particularly fearful of such things, arm yourself with knowledge about "lions and tigers and bears, oh my". Plus maybe snakes and scorpions. I don't put this particularly high on the list, but some folks are more comfortable knowing the statistics and what causes actual issues that really happen.
More critically, know about creek crossings. These actually can be dangerous. For the PCT, the Sierras are where the issues are.
Know how to hitchhike. There are various skills here, not just about getting a ride, but knowing how and when to decline one.
Ice axe. Know (body knowledge, not just head knowledge) how to self arrest and self belay. Also know when to bail, when to turn back to save your life. Extra emphasis on this aspect if you're young and male.
Know how you want to keep a journal; different approaches here, but you'll be happier at the end if you keep at least some notes along the way. Ditto knowing how to use a camera of some sort.
Optionally, knowing how to use the cell phone you carry --- whatever features it has that might be useful on trail (especially if a smart phone), take significant time before the trip to learn and practice with.
Know how to sleep warm without carrying a ton of gear; there are some tricks. Look them up, learn them.
Know how to deal with bug swarms. Again, there are different approaches, best if you have some clue ahead of time.
Know how to recognize poison oak, in its various phases --- look for pictures on the internet.