Remeber the Fielding capoing lore.

1. Never capo tighter than you absolutely have to.
2. Put the capo as close to the fret as possible - I take this one stage further, and aim to get the very edge of the capo rubber actually pinching the string to the fret, but not so far forward as to damp the string.
3. Put grooves for the fat strings in a capo to be used on a 12-string, otherwise the fat strings are bent more than the thin ones and go sharp.