Everyone fills in the basic facts in iTunes for their songs -- name, artist, and usually album -- but don't forget another valuable piece of information, the track number!
Track number is important when you're burning an audio CD. You'll want to sort by that field to avoid the songs coming out in alphabetical or some other unhelpful order. It's important when you want to verify that you have all the tracks from an album. When listening to the album in iTunes, you can sort the songs and turn off Shuffle to re-create the album experience. Ditto on your iPod, if you turn off Shuffle or set it to Shuffle Albums, and listen to songs in album order.
If a group of songs don't already have the Track Number field filled in, don't give up hope. A couple of Applescripts let Mac users of iTunes fill it in without a lot of gruntwork.
Use the first script if your song names in iTunes are stuffed with several pieces of information, including the track number. Typically, all the songs from an album will use the same format for the name, for example "01 - Happy Birthday - Greatest Birthday Songs" or "5. Christmas Album / Jingle Bells". But each album might use a different format. That's where the Track Parser script comes in. You select some tracks, enter a coded string that says how to interpret the data, spaces, and punctuation in the names. The script scans through the selected tracks and slots the information into the right fields, while stripping that extra information out of the name field. You can experiment by doing "test runs" on a single track before you turn it loose on dozens of songs. And you can save the string patterns, so that if you encounter similarly named songs in the future, you can "decode" them just by picking from a list of sample song names.
If the track information isn't in the song names, all is not lost. You'll just need to do a bit more work. First, you'll need to download and install the Albumize Selection script. Go to Wikipedia, Amazon.com, or some other "discography" site that lists all the tracks on that album. Turn off Shuffle in iTunes, put the tracks in a playlist, and sort that playlist by the first column -- the one with no label, just numbers. That puts the tracks in the order that is iTunes' "best guess" of the right order. Once these settings are in effect in the playlist, you can drag songs up and down to reorder them. When they're in the right order, select all the tracks from the album (or from disc N in a multi-disk set), run the Albumize Selection script from the iTunes script menu, and it will fill in the "Track X of Y" information for the selected songs.
If you have to go to these lengths to find out album information, don't forget to also fill in the year for all the songs in each album. That will let you create Smart Playlists based on year or decade, and sort an artist's work in chronological order.