Besides the obvious about going to class....
son had a possible opportunity to get drafted out of HS. For him, the better option would be going to college, do some growing up and enjoying the entire college experience. He loved the experience and will most likely always remain one of his life's best experiences.
Also keep in mind that they may mess up once in a while, but that's part of it, growing up, and most of us have been there so we understand the lumps and bumps you take learning to live on your own. If they have an issues or a problem, be there to listen, that's what they need more than anything and don't give advice unless they ask for it.
Big adjustment for everyone, he/she misses you but you miss them more because maybe your life isn't as busy as it used to be, keep things in perspective, it's not about us grownups, it's about them. Find new interests or revive old ones.