Well I can share my 2 pence on how I handle classical music. Might not be the "proper" way but it works for me... Pardon the overkill level of detail, but classical music is certainly a beast to deal with digitally!
I try to get as much info from AllMusic.com as possible. For track titles I usually refer to the publisher's website for consistency, and album art I use whatever source has the largest (around 500x500 px) size.
- Multiple genres are used. Primary genre is the classical "era" in which it was composed. Usually looking at the composer profile on AllMusic.com will indicate their era. Otherwise I use this as a general guideline - Medieval (up to 1400), Renaissance (1400-1650), Baroque (1650-1750), Classical (1750-1820), Romantic (1820-1900), Impressionist (1870-1915), and Modern (1910-present). Secondary genres could be the type of composition or instrument- e.g. Concerto, Symphony, Ballet, Piano, etc. I also always include the genre tag Classical for file organization rules.
- The performer is used - e.g. London Symphony Orchestra, except for Various Artists albums, where the composer is used.
- Multiple pieces are separated with a "•" symbol, and the conductor is added at the end in parenths - e.g. The Seasons • Chanson Triste • Song Without Words • Nocturne (Ilona Prunyi).
- Album Artist
- The composer is used - e.g. Pyotr Ilyich Tchaikovsky. For albums with more than one composer I generally use the composer with the most pieces on the album. I use Various Artists for theme or mix albums where all composers are different.
- For single-composer albums, I use the full composer name. For multiple-composer albums, I use last names and separate with a comma.
All the music, including classical, in my library is auto-organized thanks to MusicBee. I have a general rule set up for all music, and then classical and various artist albums use rule exceptions so they're handled differently. Classical track titles can be really long, so I just exclude them altogether from the file name, and reference the tags instead when needed. Also this is where it is important that all Classical music has a genre tag (doesn't have to be the primary one) of "Classical" so it can be organized into a top level folder. Here's my methodology:
<Genre>\<Album Artist>\<Album> (<Year>)\<Disc-Track#> <Title>
- Genre is "Classical":
Classical\<Genre>\<Album Artist>\<Album> (<Year>)\<Disc-Track#>
- Album Artist is "Various Artists":
<Genre>\<Album Artist>\<Album> (<Year>)\<Disc-Track#> <Artist> - <Title>
- Album Artist is "Various Artists", Genre is "Classical":
Classical\<Genre>\<Album Artist>\<Album> (<Year>)\<Disc-Track#> (<Artist>)