1. Context matters. The context in which the adaptation (translation, song setting, theatrical performance, film adaption) occurs is never that of the original work. But we can never receive the original work again originally (if it is from another epoch).
2. Medium matters. It makes a difference whether it is film, music, a poem-to-poem translation, etc...
3. The adaptation adds and subtracts. It never transmits the same information. It always leaves something out and adds something new.
I know there should be about five or six maxims, but I don't know what the other ones are yet.
[UPDATE / May 21]:
4. There should be something about some of the information given by the adaptation is trivial. In other words, it is perfectly possible to do a reception / adaptation study and find nothing at all interesting. Put another way, it takes imagination to see the possibilities of this kind of work.
5. The comparison is never two-way, between the original and the adaptation. It is always four way:
The relation between the original work and the original audience
The relation between the adaptation / translation and the audience for this.