Yes, as others have said.....keep it FUN. Look online for some games you can play with him as he hits off a tee. It might get to the point where when you get home from work or on the weekend that going to the ball field with your son is what you look forward to more than anything else. If this happens make sure that he's the one asking to go to the ball field not the other way around. When you're asking him to go instead of him asking you then that's when you know he doesn't enjoy it anymore. If this happens then move on to the next thing that has peaked his interest.
As I'm sure you will, make sure he's exposed to different types of sports. Also make sure he plays in the dirt with Tonka trucks, builds forts, shoots a pellet gun and READS.....anything. Just make sure he READS. Start reading to him every night if you're not already doing this (I'm sure you already are) and not just one book a night but at least 2 books a night. 3 if time allows. If he's a reader there's a good chance he'll be a leader.
Record as much as possible....if you can't record cause you're playing ball with him then make sure your wife or your father-in-law or someone can be there to record these moments because as everyone has already told you, it goes by too damn fast and you'll look back when he's 15 and think how is he already 15?
Unfortunately, if you don't record these moments you are more than likely going to forget most of them. We were able to record a good bit of my sons activities during these years but wish we'd have recorded more.
Sorry for the LONG/SAPPY post but this got me thinking back on my son and all the activities he and I have done together over the last 14.5 years.
Have a blast cause you're about to go through some of the best years of your life. Wish I could do it all over again.