For accompaniment tapes, it is easiest for me if you provide a CD (or tape) of the original performance along with the printed music. CDs are better because they are in tune, where tapes may be slow or fast and out of tune with my equipment. If the printed music is not available, I can reproduce the parts by ear, but that is a little more time consuming.
For digital edits such as cuts for dance studios or cuts of your prerecorded accompaniment tapes (eg. take out a verse), it is best to give me instructions based on time. Telling me to cut from 1:31 to 2:18 out of a song is good and results in a precise and accurate cut. Telling me to cut after the background singer says "huh" is less accurate because she may say it three times.
If there is a question concerning an arrangement or a cut, it is often helpful for me to call you and play the song over the phone for you to preview and make suggestions +/or changes.
And, as you might expect, giving me plenty of time is always appreciated.