Several years ago, a friend of mine named Matt Preira wrote a piece for the Underfoot webzine called "The Art of the Mix Tape." It was one of my favorite things I've ever read and inspired me to pick up a hobby I've been enjoying for roughly a decade now.  Mix tapes or mix CDs are always a fun little gift for someone special or even for yourself.  But they can't just be thrown together willy nilly in a random order of randomly chosen songs.  Great care and time should be taken both in choosing as well as re-ordering the songs and making them into a tape or disc.  Also, with the advent of digital music and portable devices to play it on, the concept of mixes has evolved into the concept of playlists.  But whether you're dealing with analog or digital music, there have to be some rules--or guidelines, if you will--that should be followed to get the best results out of your mixes.