Let's be honest: he is probably going to give you his advice whether you ask for it or not, but it just works so much better when you ask! Ask for his advice on Church activity, on classes, on friends, on school, on dating, on sports or other hobbies. Ask for his counsel on your Church assignments, on preparing for your mission, on decisions or choices you have to make. Nothing shows respect for another person as much as asking for his advice, because what you are really saying is, "I appreciate what you know and the experiences you have had, and I value your ideas and suggestions." Those are nice things for a father to hear from his son.
In my experience, fathers who are asked for advice try harder to give good, sound, useful counsel. By asking your father for advice, you not only receive the benefit of his input, but you also provide him with a little extra motivation to strive to be a better father and a better man.