Congrats! When is s/he due?
IME, supervision and proximity are key. Shadow was 4 when my daughter was born and did GREAT, never had any issues at all. She could tell that the baby was a part of the pack and began "guarding" her almost immediately. I now have a puppy and a toddler which is different in many ways, but requires equal supervision (if not more on the human e I would definitely recommend putting up baby gates early to separate them if you can't be in the room (showering, cooking, etc.).
Do you have any specific questions?