So if you have already recorded, the next steps before sending your songs to mix are:
Edit your tracks: your tracks must be edited (for example if the drummer's performance needs tightening) before sending them to mixing. If vocal tuning is needed, I can do that here (but that's an additional service).
Clean up your tracks: remove unwanted noises, and send me the right takes. If it shouldn't be heard on the record, then you shouldn't be sending it to me without a very clear explanation of why it's been included.
If you used Virtual Instruments, bounce them to audio files.
Consolidate regions, items, clips or whatever your DAW of choice calls them, so that all files start at bar 1. That way, I'll just have to import the files and everything will be aligned perfectly in Pro Tools. This is the simplest way to transfer your material, even if some of the time it might mean that a guitar solo has 3 minutes of silence before it. You can use wav or aiff format.
Pro Tip: if you zip your files, all silences will be compressed to almost nothing, so you'll gain A LOT of space.
Export mono sources to mono and stereo sources to stereo. For every mono source you send as a stereo file (doubling its size and e-carbon print for nothing), a dolphin dies.
Rename the files using a convention that will make sense for someone who is not in your head, and keep this format consistent throughout all your songs.
I can't stress this enough: please make sure that you've included only the correct files and that nothing is missing. You should test each song by importing the files into your DAW and check that everything is present and aligned. It may sound obvious to you but trust me, it's not so obvious to most.
If you recorded to a click, export the tempo map and any time signature changes as MIDI files for each song, and include those files. If there's just one tempo for one song and it's all 4/4 then just make a note of the tempo value.
Create one folder per song, then place any audio files you want me to use in a folder called "Audio". Please don't put files in subfolders like "Drums" or "Guitars", just name the files mindfully.
If possible, include a rough mix of each song. I might want to refer to it to figure out what's the main line, the lead instrument, where the emphasis should be, etc. If you don't have rough mixes but know what you want or what you DON'T want, make notes for me in a text file.
Of course, you can just leave all that up to my interpretation. If I'm wrong, don't worry, nothing is undoable. Feel free to include an extra folder containing some songs from other bands that you like the sound of. I'll keep that vibe in mind as I mix, but I'll always stop short of making you sound like a clone.
If your songs contain very complex choir parts, intricate 200+ tracks of samples, or heavily orchestrated sections, my advice (if you can) is to premix those and send me stereo stems. Put those stems in the main "Audio" folder and the original rough files in a separate folder called "Slave".
And finally, tell me which song you want me to mix first. Choose one that's representative of your music, one that sets the tone for the whole collection of songs that I'll be mixing for you.
When you're ready, compress each song in a zip file and share them with me online (WeTransfer, Google Drive, iCloud Drive or whatnot, just please don't use Dropbox, I hate it...). If your internet connection is not reliable enough, put all of those files onto an external USB hard drive and send it by mail. No matter what, always keep your own copy of those files in safe places (yes, you should always have several backups in different locations). Keep in mind that I will not send your drives back.
Once I receive the files, I'll work on the first song and upload a mix to my secure private server. It will then be up to you to tell me what you like, what you don't like, and what I should change. Some mixes can take a few trials and errors before they'll meet your expectations (especially if you know exactly what you want), so don't be afraid to give me your honest opinion.
The advantage of this unattended mixing process is that you will be able to hear the mixes in listening environments that you know well (your home studio, your car, on your buddy's hi-fi...) as many times as you need. We'll systematically work through and hone each song to perfection in turn.
I generally master my own mixes as I go, but if you want to have your material mastered somewhere else, I will provide the unmastered mixes. Exported stems (separated mixdowns of your drums, bass, guitars, etc) are possible at a small additional fee.