- Variation. It's good to change things up a little. You don't want a whole lot of fast loud songs in a row, or a bunch of slow thoughtful songs all together. Two adjacent songs shouldn't be in the same key if you can help it.
- Key compatibility. This one is a little harder to explain to nonmusicians without an audio demonstration, but certain keys work together better than others. If you've just played a song in G major, and your next song is in C major or F# minor, it will flow well. From C major to F# minor, on the other hand, is a little jarring.
I've been aware of this on some level before, but as I construct our latest set list, it srikes me that I tend to write certain kinds of songs in certain kinds of keys. If it conveys, I don't know ... a softer emotion like contentment or wistfulness or melancholy, it's more likely to be in a key with sharps, like G, D, or A. If it's kick-ass angry or angsty, it's more likely in a key with flats, like B flat or A flat. (And if you've ever learned to read music, you know that flats and sharps are relative -- F sharp is the same as G flat -- so none of this makes any real sense.)
Do other musicians have different keys for different moods, or is it just me? And does the key a song is in make any difference whatsoever for listeners?