Clean up your tracks
Makes sure there is nothing on any of the tracks you wouldn't want in your final mix. This could be dead space between verse and chorus on a vocal track, back round noise, amp hiss before it's part etc.. Do proper fades and silence anything that isn't supposed to be there.Check your crossfades. Make sure there are no clicks or pops between regions in your tracks.
Timing and Pitch Correction
Timing and pitch correction are not included in the mixing process. Make sure to have that taken care of before sending files off to be mixed. Editing is billed at the current hourly rate unless otherwise specified specifically.
Export your WAV or AIFF Files for each audio channel. Each instrument,vocal, or effect/sample should have it's own track. For example: if you have 32 channels in your project, you will export 32 WAVE/AIFF files. Make sure to name each track with an easily identifiable name (kick in, kick out, snare top, snare bottom, lead vox, etc).
All channels prepared for export should have all plugins (EQ, Reverb, compression, etc)should be removed. Regarding creative effects such as delays and filters; create an additional track with the instrument name and the word "demo" prior to export. This will allow for use of the provided effect, or at the very least a reference.
Turn off all bus/master bus effects.
Make sure none of the audio files are peaking above -1db.
Send in whatever format the audio was recorded in. For example: 24bit 96k or 24bit 44.1 (MP3s will not accepted)
All exported audio files should be the same duration (no matter where in the song said audio file occurs). You can check to see if the files have exported properly by opening a new project and importing all the files with the same start time. If all the elements are in their proper place along the timeline you are good to go.
Rough Mix & Reference Tracks
If available send a rough mix as well as one or two reference tracks. A reference track being an already mixed and mastered song you would like to be referenced against your song. This simply helps us get on the same page with regards to expectations.