Customary prefix for custom keybindings

[Kyle Sexton]

All,

Is there a customary prefix for custom keybindings?  For example, say I
have a key binding that I want to setup for 'foo' mode, should I use
something like 'C-x f <key>' or 'C-c f <key>'?  I've seen C-x and C-c
used, but would rather not clobber other keybindings so would like to
use the customary prefix if possible.

-- 
Kyle Sexton
ks@mocker.org