Don't let your dog run up to a leashed dog while saying, "It's OK, he's friendly." Your dog may be the friendliest dog in the world - the other person's may not be.
When my dog jumps up on you, and I say "Gracie, get off," Please don't say, "That's OK" and encourage her. I am not apologizing to you, I am trying to train my dog. Please do not sabotage my training.
When walking on a mixed-use trail, if you hear or see a bicycle coming, call your dog to heel and move to the side of the trail. (You'd be surprised at how many cyclists have thanked me , in a surprised tone of voice, for doing this.)
At dog shows, strollers, especially the big ones, are not a good idea. You want to be able to scoop baby up away from face-licking dogs. Not to mention that male dogs might lift their leg on it. (Show dogs are not fixed, and there is usually at least one female in season present, so most of the boys will want to mark anything that sticks up.)
Most people at dog shows will be happy to talk abut their dogs and their breed - but not when they're waiting to go into the ring. They will be trying to settle their dogs down and get them to focus.
Always, always, always ask before you pet someone's dog, and teach your kids to do so too. And take "no" for an answer.