The easiest way to choose a mix engineer is to just listen to their work. Below is a link to Red Vault's Soundcloud account where you can listen to some of our work.
If you tracked your project in Pro Tools, you can simply compress your Pro Tools folder where you've recorded all your songs and upload with the link below. Make sure all of your audio files are present in the 'Audio Files' folder. Additionally, make sure all of your tracks in your timeline are clearly labeled
If you're using another digital audio workstation such as Logic, Cubase, etc., consolidate all of your tracks from zero (the start of your session) so all of the files line up correctly. Label each file and export to a separate folder keeping the sample rate and bit rate the same as the session. DO NOT CHANGE. Before you consolidate make sure all of your files in each track are properly crossfaded together to avoid clicks and pops. Do this for all songs making a separate folder for each one. If you're confused, send us an email and we can walk you through it.