It is hard because if you act too overprotective they will sense that and might act scared, but if you aren't protective enough, he might get hurt. When I introduced Mia (1.5 lbs) to my roommates new dog (she rescued a 35 lb cocker/golden retriever mix) I was so nervous, because Mia LOVES everybody and every dog she meets, and always wants to play immediately. I got on the floor with them and Mia got up on my lap so she was on Bailey's level, they sniffed each other, and after that he was very gentle with her. He does have a very gentle personality though, so I would just get there and evaluate the dog's personality.
And now look who are the best of friends!
http://www.mylittlemia.com/Mia_Bailey_111.jpg http://www.mylittlemia.com/Mia_335.jpg