I make sure, first of all, to not freak out if I see a big dog. Because they will BOTH sense it and that will make them freak out.
If the dog comes up to me, I will put myself between it and Tucker (Tucker is 12-14 lbs, I'm worried that if a dog were to jump on me I would drop him, so instead I put him behind me). I meet the dog first always, unless I have a bad feeling in which case I'll just take Tucker away. But I figure, hey, he needs some friends. So I'll let the dog sniff me, I'll talk to the owner, pet the dog, then slowly introduce Tucker.
I don't let any dog just run up to him, but I don't want to avoid every dog I see, either. Of course, if I see a dog that I'm just NOT comfortable with for whatever reason, I'll just walk away. But if I have an ok feeling about it, then we'll give it a shot.