I think the main thing is to instill in a child love of Torah. Like other posters said, setting a good example for him is paramount. Also, encourage him from when he is small. Ask for his participation in discussions at the Shabbos/dinner table. Go over what he learned. Encourage him to learn with you – make this fun and interesting. Ask him to prepare/share a vort at the Shabbos table.
If he loves learning and either 1) he is brilliant and it comes easy, 2) he is not brilliant but he really wants to persevere, then he will hopefully learn to love Torah and learning Torah. Once that cycle begins, then it will be up to his parents to nurture it and not stunt it and give him the best opportunities to grow to be a godol B’Torah. I don’t think you can do much else except give the opportunity and water the fertile ground that you create. Everything else is out of your hands.