First, start with a couple of small manageable collections, not large collections. By small I am suggesting 100-200 images. At this point, you have little if no experience working with digital images and CONTENTdm. Why start with large collections that are more unmanageable than you realize. With small collections you can easily make corrections to the records and you will get experience using the software, the controlled vocabularies, and the general feel for the workflow that will be involved. Changes will constantly being made as this is a trial and error period.
Second, work with collections that are not just processed, but also have been researched. At the same time don't assume a processed physical collection will be organized in a manner conducive to a digital collection. What's in a box together doesn't necessarily equate to an organized collection. Having the research done also helps tremendously. Otherwise you are constantly stopping to do more research which interferes with the workflow.
Third, get more than one person's perspective from the very beginning. Each person brings different work and life experiences to the project. No single person can recognize the multiple perspectives that a image/collection can be viewed from.
Fourth, be selective on what you are digitizing. Ten images of the same building from slightly different angles does not improve the digital collection.
Fifth, think outside of the box. Just because they are in the same archival collection doesn't mean they have to be in the same digital collection. When a group of organizations are working together on their digital collection website it may make sense to pull photos from a variety of collections to create a single new digital collection. An example might be a collection of 1906 San Francisco earthquake photos. If multiple organizations have photos of this event it may make better sense to pull them together to create a new digital collection.
Sixth, communicate with everyone working on the project. Communication is crucial especially in a consortium site. It's a team project and everyone's thoughtful input can only improve the digital collections.
Seventh, take your time. You want to continue to move forward, but you don't want to sacrifice quality for quantity. And you don't want to always be backtracking and making corrections.
I could probably keep on going with this list, but my hands are tiring.