One thing that no one mentioned so far is that all the dog parks I have been to expect you to clean up after your dog. The places I go have their own bags and a recetptacle to put them in.

All the dogs run to meet the new guy so it is easier if you hold your dog back either physically or verbally so that the new guy isn't overwhelmed by all the others sniffing etc.

It's your responsibility to make sure your dog doesn't get too rough with another dog. That doesn't always being mean. I have seen several dogs hide behind their owners because another dog just is too rough for the other dog. Snoopy isn't exactly a shy dog around other dogs but there is at least one other dog I can think of that he hides from because he plays too rough. If you see other dogs hiding or running to their owners to get away from yours, you may want to work with your dog.

Don't let your dog jump on other people. (that's a tough one because if someone has treats mine still do at times). Watch giving out treats. If the dogs seem to be getting too competitive about getting the treats, put them away for awhile.

For some reason, a lot of the dog "fights" have started underneath or around the picnic table. Some dogs think that when they have claimed a place to lay or hide, it is theirs and they don't want intruders. When too many dogs start congregating in one area it is time to "walk" some of teh dogs into another area.

I am sure there are other things I am forgetting but those are the ones I can think of now.