I'm quite a tidy individual especially when it comes to my hard drive.
I also keep all my 3,000 or so MP3s in the same folder. This is for two reasons, firstly it makes it MUCH easier to just browse through them all, secondly, when I'm backing them up onto CD-R, it means I can just select 700MB's worth and burn them, instead of having to cobble together various folders to the same amount - occasionally splitting folders up when they turn out to be too big, and putting stuff in non-alphabetical order. (Why does Windows not display folder sizes? WHY?)
But finding a consistent filenaming format is difficult, when you want to keep your tracks in a sensible kind of order.
AlbumArtist - Year - AlbumTitle - TrackNumber - TrackArtist - TrackTitle
Pink Floyd - 1975 - Wish You Were Here - 03 - Pink Floyd - Have A Cigar
First we sort by album artist. The album artist is almost always the same as the track artist, but there are a few important exceptions. For compilation albums the album artist is "Various artists". For movie soundtracks, the album artist is "!Films" because I like my film soundtracks to appear first in the list. I put "[unknown]" if the album artist is unknown (this is rare, but it does happen). I don't just put "unknown" because there are several tracks out there which are actually CALLED "Unknown" and it could get confusing.
The year given is always four digits: this means that I get to listen to the artist's discography in release order. If the year is unknown, I put "0000". For movies I put the year of the movie here. If there were several albums released by that artist in that year then I add a letter on the end to keep them in order, e.g. "1999a", "1999b" etc. This is usually a bigger issue in the case of movie soundtracks than anywhere else.
The album title is next. This is pretty obvious. Once again, if the album title is unknown, I put "[unknown]". If the MP3 I'm listing is not from an album but from a single or EP or something, there's no reason to deviate from the norm. I classify a single like a three- or four-track album.
Track number is next, and again, I put "00" if I don't know it. For albums which come on more than one CD, I don't bother putting "CD1", "CD2" anywhere - I just continue the track numbers from the first disc to the second. For example, The Best Air Guitar Album In The World... Ever! has one CD with 20 tracks and one CD with 21 - under my naming scheme that becomes one big, 41-track album.
Track artist is where it gets interesting. Usually this will be the same as the album artist. But sometimes you come across a remix or a duet or a collaboration or something. For example, Linkin Park released an album of remixes called Reanimation. For that, I'd put "Linkin Park" as the album artist, but the name of the DJ or DJs who remixed the track as the track artist - that keeps all the tracks together in the right album, but also lets me see who really made each track. Or a live version of Comfortably Numb which Pink Floyd recorded with Trent Reznor would have "Pink Floyd" for album artist but "Pink Floyd with Trent Reznor" as track artist.
Lastly is the track name. Nothing special here.
Obviously there is a file extension on the end too.
Generally I duplicate names as accurately as possible. Lots of artists/tracks have names containing nonstandard or illegal characters like "*", "/", ":" and the already-used delimiter, "-", so I make do with commas and whatever other characters are allowed. Usually for things like umlauts I dig out the correct character though.
For tags, things change slightly. Tags usually give you fields for "Title", "Artist", "Album", "Year" and "TrackNumber", which I find to be inadequate. (They also give other guff like "Genre" which I never bother with.) Here's how I get around this:
But here's the clever bit. The track numbers and years are just there so that the MP3s stay in the right order in my Music folder. I'm not really interested in seeing them on my playlist. Instead I set up my Winamp playlist to display in the format "Artist - Title". That way I get to SEE
AlbumArtist - AlbumTitle - TrackArtist - TrackTitle
Pink Floyd - Wish You Were Here - Pink Floyd - Have A Cigar
So if I sort by "Path and filename", I get all the MP3s in the same order they're in my Music folder. If I sort by "Album" I get the files in roughly the same order, but still separated into albums. But if I sort by "Title", all the tracks from compilation albums and movie soundtracks, for example:
!Films - 2004 - The Bourne Supremacy - 13 - Moby - Extreme Ways
...get grouped back with all the other Moby tracks, enabling me to find all the Moby stuff, even the stuff which isn't on Moby albums, very easily!
Like all filenaming/tagging formats this format is not without its drawbacks but it's served me very well.
I'm not going to lie: implementing rubbish like this on a four-figure MP3 collection is a lengthy proposition. I happen to take pleasure in such things, but that's because I'm a freak.
I've yet to find a free piece of MP3 tagging software which does everything I want it to, but for renaming files (not just MP3s, but generally), I unreservedly recommend Jim Willsher's Bulk Rename Utility. It's not just free: it's tiny, user-friendly, monumentally powerful, doesn't need installing, and accepts Regular Expressions. I use it all the time. Highly recommended.