What you should do
Firstly, I encourage you to send your own raw mix of the tracks, along with as much written information as possible about what is wanted, so I can easily evaluate the project.
You must deliver WAV or AIFF files in 24 bit and 44.1 kHz of each audio track/instrument.
Every audio track must be clearly named with what instrument it is, and whether it is a stereo or mono track.
For example, 'guitar-rhythm-left.wav' would be a mono track of a rhythm guitar being played on the left audio channel.
If there is an unusually large amount of provided audio files (16-20 should usually be enough), or they have a messy naming convention, the price of the project could potentially increase.
All audio tracks in a project must have the same starting point.
Audio tracks must if possible be delivered with no added effects, such as reverb or compression.
Please describe which effects are required, and where they should be placed, if any.
I recommend delivering a "dry" version of an audio track (without effects) along with a track with any desired effects.
And please keep in mind that mixing and mastering isn't a magical process in which poor audio recording becomes great, so make sure you to always make your recordings as good as possible.