But what impresses them the most is whether he looks like he is going to be a success in life. So tell him to build up his interests, his social life, and his studies. And to have some clear ideas about a career (you will enjoy telling him that bit, though he will probably zone you out!).
Okay, he must also learn to understand girls and how to treat them right. But once it is clear he is destined to succeed, and is confident and having fun, then it is the girls who will come looking for him, not the other way round!
All the best,