How to organise MP3 singles
There are two types of 'singles' encountered in digital music collections. The first type are genuine single releases - three or four tracks released by an artist as one release. Normally they contain a main 'A' side and a few 'B' sides. The second type are where you've built a collection of odd tracks from an artist with no containing release. These tracks could have been downloaded online or selectively ripped.
Perhaps surprisingly, the latter requires more thought than the former.
The former, official single releases, can be treated identically to your other albums. The 'album name' tag should be populated with the single release name. I think the use of the word 'album' in the tag names of many file formats is misleading, 'release name' would be better, but this is a historical artifact we are left with. All other album rules should be followed for single releases. Single releases also generally have their own cover art, which should be applied consistent to the rest of your collection. This way, your single releases will be displayed alongside other releases. File organisation should also be the same, with single releases sitting as peers or siblings in the directory/folder structure with albums.
Less straightforward are the 'miscellaneous' tracks. If you want to separate these from other tracks I suggest leaving the album name blank, otherwise they will appear in your music player as an album under the name chosen. Track number is also irrelevant. However, the track name should be populated, as should the artist name.
For file organisation, I think the odd tracks should appear in an artist folder. Cover art is more subjective, you could choose the single art if the track was ever released on a single, or maybe the album art on which the track has been featured. In some cases, for instance classical works, you could choose an image depicting the composer, performers or conductors, but this is personal preference.
Whatever you choose, it's worth thinking about the consistency of your single track organisation, because otherwise they are easily lost in your collection and easily disorganised.
Thanks to chinnian and coddobblog for the images above.