let's see.....
Without tying you up: I either sit on your ankles while you're on your tummy and let my fingers or feather tickle your soles, arch, anywhere that's possible. I'll somtimes reache over to tickle somwhere appropriate for you like legs, thighs ribs, etc.
Tying you up: My favorite bondage is tying your feet together and your wrist together (either above or below your head). Then I enjoy tickling your feet with however's approprite for you.
P.S. I sometimes may end up using my tongue if it's ok...if not, then I won't do that.