Here's where I'll ask all overly specific questions, now and hereafter. 

I've got a potential stud in AA right now. I'm told (by pretty poor advanced scouting) that he has potential durability of 100. Right now he's at 68. I know how to improve fielding (get the man some friggin' reps!) and hitting (get the man some friggin' reps!) but how should I go about improving durability? A lot of rest? A lot of PT? 
Sincerely,
Lost and Confused

Durability is a rating that improves or declines (for older players) in between seasons, and is directly related to your training budget.

Maximize your training budget. And don't worry about overly specific questions. It's all about the details.

FYI if this is his first full year, then a 68 dur has a lot of room to improve. By year 3 or so, it's pretty much locked in, maybe 1 or 2 points to improve.