Most of the good advice has been covered above by some great people that helped me along the way. My 2 pennies....
1. Take it all in. Of course, everyone wants their son to get innings and contribute, but for many, especially freshman and at times sophomores, playing time can be limited. Enjoy seeing your son in a college uniform and representing that institution.
2. Try your best to make your trips to games enjoyable, whether your son is playing or not. Have to have the mindset that your rooting for not only him, but his school, and teammates.
3. You will meet both even-keel parents and those that still think that it is high school baseball. Be polite but steer clear.... way clear.
4. As most parents will do, just be supportive in every facet: academics, physical and mental well-being...and all that goes along with the responsibilities and mental toughness required of a student athlete.
5. Get ready for some great stories. At least the one's your son will tell you about.
Good luck.
WCP