Roles and the aligned skills with those roles.Classes and what weapons the classes will use.Whether you change from what I've recommended (as I do have multiple options for some companions) or you change them entirely. You can always change what each characters classes and roles are. In advance, I will say that this is suited to my play style, thus my opinion on what I think fits best with whatever.
This was made for myself, but thought it would be helpful and cool for others to see. This took me awhile but I felt this was necessary to do. A brief guide on classes, roles, companions and groups.