Not an expert. Just learning myself but as a rule of thumb I try to make all my tracks mono. They seem to sit better in a mix. The exception being piano or keys. They always have a stereo effect or sound.
Bass always mono.
Vocals always mono.
Guitars mono. Usually double up with a left & right for rhythm and I usually play them slightly different with a slightly different tone. Guitars stereo when they have stereo effects such as stereo delay.
Drums should be all seperated and mono
Keys usually stereo
Of course there are exceptions to the rules. It depends on effects or dry. How many tracks your working with etc. Whatever works best for you.
As for panning I generally pan my guitars any where from 30% to 100% left & right. Many times I find 69% the magic number for me. Or I just like that number
Lead guitar to one side or down the middle. One song I'm working on the guitars just don't seem to work well panned at all. They sound best in the middle. Strange. I think you have to let your ears be the judge. You want to find space for each instrument without overlapping and making mud of it all. It's not easy.
My 2 cents
Dave
