Clean files, honest references and one person who gives the notes. That is most of it.
Mixing someone else's recording is a conversation, and like any conversation it goes better when both sides know what they want.
Files
Every track starting at the same point, named so a stranger can read it, at the sample rate it was recorded. Print your effects only if they are part of the sound.
References
Two or three songs you love the sound of, and one sentence on why. A reference is not a target, it is a direction.
Notes
One person collects the notes from the band and sends them in one list. Two rounds are in our price, and most mixes are done after the first.

