Thank goodness skiing is not as bad as golf in this respect. If golfers got advice from "everyone" they'd go nuts. It's probably time for your friend to start thinking quality vs quantity.
Instructors trained in PSIA methodology teach skiers of all levels to develop 4 basic skills: Balance, Edging, Rotary and Pressure. Balance is the most important. In the first lesson, we give students exercises to develop all four skills. As students progress, lessons may focus on enhancing a specific skill. But please understand that we teach movements (not skills). In my experience I have not found any one thing that is hardest to master in the first year or two because people with so many different life experiences take up skiing. Some people get it right away, some people struggle, some people need step by step coaching and some people just need mileage.
Instructors try very hard to not approach lessons with a cookbook formula (e.g. every advanced beginner should work on "x"). We'd rather ask your friend where he wants to go with his skiing (point B), look at how he currently skis (point A), then draw the line to map out what it will take to get from point A to point B. Many students at this level will simply say they want to "turn better". In reality, that may translate into skiing more efficiently, smoother, faster or more comfortably skiing steeper terrain. But those things could just as easily require working on equipment or emotions as teaching different movements. We used to say that advanced beginners were working on transitioning from wedge christies to parallel turns. Shaped skis have given us many more options for how skiers can progress from beginner to expert. Finally, not everyone has the desire, time or money to become an expert skier. It may be that the best thing for your friend to work on this season is simply "having fun".