1) Bring plenty of water for both you and your dog - too much salt water can cause problems.
2) Bring a blanket, and umberella for sunblock if possible - hot sand, paws, and feet don't mix.
3) Expect to get visited by other peoples dogs - and by other dog people.
4) Bring pick up bags - to clean up after your dog. Not only is it the law, its also a health hazard to fellow canine visitors/people and the environment.
5) Have your buddy wear a nylon leash and lead and rinse it out once you get home.
6) Some beaches have strict on leash policies - be aware of the local laws and follow them. If dogs can be off leash be sure your dog is practiced up on the "come" command.
7) Be aware of any beach conditions or hazards, and sand fleas.
8 ) If your dog likes to play fetch - bring a float-able toy that makes playing in the surf more enjoyable.
9) Take lots of pictures, especially if your buddy is wearing something from TootsUncommmon.
10) Rinse and/or bath your dog down when you get home.