My experience is this answer will change for every Wardrobe Department. The team I've worked with most often, most recently, gave me the form they use, which is a simple entrance/exit form with columns set up in the following way:
Actor Name - Character/Part - Time & Location of Exit - OUT of X look INTO Y look - Time & Location of Entrance
In the column describing "OUT of/INTO," I typically give basic info. "OUT of Lost Boy INTO Blue Pirate look" is perfectly sufficient to tell the Wardrobe Supervisor about the change.
As far as determining where changes will be executed, of course, decisions will vary according to your team and venue. The rule of thumb that works for me, here, with this team, is that if the interval of time for a change is great than 4 minutes, it's done in a dressing room. If it's less than 4 minutes, we will do the change on deck, at the place most convenient to the actor's next entrance location.
In our current show, several actors wear flying harnesses, and several also have extensive makeup/wig changes. We've determined the best practice is to always treat harnesses as deck costume changes, so the designated flight captain can check them without leaving the backstage. Massive makeup changes are always in dressing rooms, often with dresser assistance.