I think the only two things you can do
-Avoid stress at all costs
-Ensure decent blood flow around your head (Can be helped by sport, massage, combing your hair)
Both these can be helped by doing sport - and from what I seem to have noticed sportier / more active guys have kept their hair, guys who aren't it's less common (And what do you know, sport reduces stress and helps blood flow). I mention blood flow because I can't help but notice the majority of hair loss is around the temples - IE where you are heavily affected by stress and get tense, and therefore likely restricting blood flow (ever seen someone rub their temples when they're stressed?). Although it's probably genetics, definitely keep those two in mind for the sake of it.