There will likely be a change in routine - such as walking at different times, feeding at different times, etc - and if you can predict anything, change it before the baby arrives so it isn't an added stress on the dog then.
I would also start implementing any new rules - such as no jumping, keeping a good distance away, what rooms can be explored or not, if the dog can go on the couch (not recommended with a baby), etc. STICK to them. In your home or any other home the dog is allowed.
Any new item - furniture, some of the clothing, diapers, toys - needs to be examined by the dog. Let the dog get used to items prior to baby's arrival - things like the bouncy seats and high chairs can be quite scary to a little dog. Give the dog time to examine EVERYTHING, both turned off and turned on.
Start working on obedience. The dog should learn that he is NOT allowed in the baby's room - a low set baby gate will block him nicely and still allow you to easily step over. The dog should learn "leave it", "drop it", and so forth so he doesn't go after the baby's toys OR any dropped food.
Start handling the dog differently. Start slowly by just tugging lightly on body parts and fur. Be a little rougher to get the dog used to it. It's also a good way or learning the dog's limits without endangering the baby or any other child.
When the baby arrives you do NOT want the dog right in it's face. For the first week i would keep the baby OUT of the dog's reach. No confrontations. Let the puppy get used to the new sounds and smells. Let the dog sniff diapers, clothing, etc. At the end of the first week let the dog sniff a foot or hand, at the end of the third week let the dog sniff a leg or bum.
NEVER let the dog near the baby's face. EVER. Not only is it not sanitary but it's asking for trouble if the dog does get spooked.
http://www.petfriendlyhouse.com/information/Children_Pets/introducing_baby_to_dog.aspx
As the child gets older, you will have to switch focus to training the CHILD as well. Write out any rules that you will be enforcing: such as no pushing the dog, no grabbing the dog, etc. The dog can have rules too, but a lot of dog behavior is tied to the child's behavior.
You should NOT allow anyone to stick their hand in the dog's mouth. Or pull on the dog's face - that's just asking for trouble. The dog may tolerate it now, or once, but may not in the future.