1. Keep the material at the highest resolution possible, if the original was 24 bit 48K, try to keep the mixes at the same sample rate and bit depth, rather than create an audio CD at 44.1/16bit.
2. Leave a bit at the head and tail of the songs. It's better to fade during mastering so that noise can be removed more accurately by using a noise profile of any existing noise at the end, and for other reasons as well.
3. A reference tone is helpful even in the digital domain to check the balance and levels of your mix. Don't fudge it. For example I've gotten mixes that are consistently hotter on one side or the other. It's difficult to tell if this was intentional without a ref tone. Tone should be -18 or -14 dbFS and marked on the mix media.
4. Documentation - includes song order, notes on the songs, things to be fixed, song spacing, sample rate/bit depth, etc.
5. If not attending the session it's a good idea to supply a reference CD of other commercial releases to demonstrate the sound that you are attempting to achieve.
6. Use professional stock for media, not budget CDs or tape.
7. Do not process the overall mix, this includes normalization, EQ, compression, etc.
8. Listen to your mixes on a variety of systems and fix any track related issues such as sibilance in the vocals or cymbals, or basically anything that "sticks out" and makes the mix unbalanced in frequency or dynamics (unless of course it's intentional).
9. Documention
10. Documentation
Just a few tips that come to mind ....