Ensure that the mixes you have approved are exactly as you want them. Occasionally, during the mastering process, one can hear nuances in this new environment that may not have been as obvious before. Though the mastering engineer will often provide one recall session to make corrections, this could become problematic if you need to return to the mix engineer for a recall of the original mixes.
Once these mixes have been approved by the artist and all of the various entities, you can request the mixer to prepare 24-bit masters. These are higher resolution, and thus, higher fidelity that will be used for the mastering. More than likely, the recording and mixing sessions were produced at 24-bit anyway. So to maintain the consistency you'll want to make sure the mixer provides these to the mastering engineer as well. The reason this may be of some concern is that usually, when printing mixes for reference, the mixer will choose to make a 16-bit mix. This is because a 16-bit mix is compatible with iPods and can be burned directly to a CD. So make sure you request 24-bit mixes. The final delivery format should be 44.1kHz/24 bit.
BWF files are preferred, as they provide a time stamp and are compatible with all software platforms. Though standard .wav and .aiff are still in great use and perfectly acceptable.
Now you'll want to apply for an ISRC code from the RIAA. This code is provided for free and will create a unique identifiable code that is digitally encoded into your master. It will allow your music to be scanned by Neilson Soundscan. Though they claim to require five business days to process your code, they are quite expeditious in their turnaround time. On a few occasions I've known clients to receive them the next business day.
You will need to provide the mastering engineer with a complete and accurate list of the artist name, album title, song titles and sequencing. It would be best to send this information via email so the mastering engineer can copy directly into his CD authoring software application. This will minimize any discrepancies in spelling for some of the more esoteric song titles.