Show him plenty of love and affection, and give his imagination plenty of play. This should have enourmously beneficial results on his long-term cognitive development, speaking from a purely physiological standpoint. You would be surprised.
If you want him to take better notes, an idea that comes to mind is making his time watching television or movies contingent upon him taking well-constructed notes on whatever he is watching. Have him write down the names of characters, draw simple diagrams to represent settings and positions, and so forth. If he plays video games, the same applies: have him use good notes to help him through his games. This is one of my more imaginative ideas, though.