No matter what keyboard or desktop environment or window manager I use, I always set the same multimedia keyboard shortcuts. This is to easily and quickly control the volume, move to the previous or next track, play/pause and toggle muting the microphone. I've settled on a scheme that is easily reachable and available on every keyboard and in my experience on the numerous desktop environments and window managers that I've tried on Linux and the BSDs, doesn't conflict with any of the default keybindings, although your mileage may vary of course.
The scheme uses a Ctrl + Alt prefix along with a single character. These single characters are all on the right side of a split keyboard, for ease.
PREFIX + U - volume up, U for up
PREFIX + Y - volume down, Y cannot stand for anything meaningful, but it is next to U
PREFIX + N - next track
PREFIX + Shift + N - previous track, shift reverses the logic of N
PREFIX + P - play/pause, P being the most obvious letter for both actions
PREFIX + M - toggle microphone mute, M for microphone/mute
This layout gives me an easy, quick and universal multimedia control interface. Depending on what you're used to, you may not like the use of two hands to operate these shortcuts, but for me, using any kind of keyboard (including a split keyboard) your hands don't have to travel too far from the home row. As well as being within easy reach, the mnemonics are obvious and universal.