The making of a great compilation tape, like breaking up, is hard to do and takes ages longer than it might seem. You gotta kick it off with a killer to grab attention. Then you gotta take it up a notch, but you don't want to blow your wad. So then you gotta cool it off a notch. There are a lot of rules.
Like any good red-blooded American music lover, I cut my teeth on mix tapes. Good, old-fashioned, analog tapes. The problem is, no one listens to tapes anymore. Conveniently, the demise of the tape coincided with the advent of the CD burner. Now sensitive guys can funnel their musical angst into a digital medium, creating a somewhat different beast: the mix CD. "Mix CD" has such a horrible ring to it, though. I'll always think of it as a mix tape. But when it's on CD, certain things change.
For one, CDs hold less music. Plus they only hold it on one side. This changes the dynamics of your message. No sweet dichotomy, not unless you're willing to burn two CDs. Another thing is, you have to burn CDs from computer files--usually mp3s, which just sound different than a tape dubbed from CDs, vinyl records, or other tapes. The different sound might make you choose different songs.
It's nice to have a theme, but it's not necessary, so long as everything has a somewhat cohesive flow. This is not to say that every song must be from the same artist or genre--that would kind of defeat the purpose. But by juxtaposing this song with that one, you are expressing something, pointing out both their commonalities and their differences. Just be conscious of that.
Apart from selecting the songs, the most important aspect is arranging them--making sure they are in a good order. As Rob points out above, there are a lot of rules. But I think most of it can be summed up by analogy to another creature of order: the baseball lineup.
You're going to want to choose a leadoff hitter whose specialty is getting on base by any means necessary. Sometimes that means a nice hit, while other times it might be a walk. The first player has to set the game in motion.
The number two is the sacrificial player. He's there not really to score for himself, but to advance the other baserunners.
By the time number three comes along, the memory of the first two is starting to coalesce into a rhythm. This third one has to tie that together and bring it home, setting the tone for the assault.
Fourth is the cleanup hitter--this is your biggest bat, your most muscle, the one who can knock it out of the park. If you can get that one-four progression to click, you're in a groove.
After that, you're free to follow your own strategic decisions. Sometimes you'll want to cool it off and start over, building to another crescendo. Other times you'll want to follow your cleanup with more big hitters so nobody can be pitched around. Toward the end it will be time for your catcher and pitcher, assuming you're playing by National League rules. These guys won't get a hit every time, but if your team is clicking, they'll round out the order on a happy note--and lead back in to another successful go-round.
Sports metaphors aside, keep in mind the primacy and recency effects. People won't remember everything in a list, but they'll remember what comes at the beginning and what comes at the end. Make these count. They serve different functions, but they are equally important.
If you are a child of the digital age taking a stab at the mix CD or, heaven forbid, the mp3 playlist, I recommend you first blow the dust of a tape deck and take a stab at that old dinosaur, the mix tape. I know, I know, it's so 1998. But it'll put hair on your chest.
Indexed by tags mix, mix CD, mix tape, baseball.