There's so much information that people could throw at you. But I would suggest that you invest $12 in Birnbaum's Guide to Disney Cruise Line. You can get it at any AAA Travel office and probably in the travel section of many bookstore chains.
It will have everything you need to know about shore excursions, dress code, check-in, passports, etc. It may not have information about the Dream itself (I think the most recent edition only includes the Wonder and Magic), but it will give you all the information you need to enjoy a Disney cruise.
Then if you have particular questions about the restaurants, amenities, childrens' areas, etc, on board the Dream, anybody here will be able to help you.