Devil's Claw can be taken dried as capsules, or as drops of a tincture. (My herb teacher prefers the tinctures as these are prepared from fresh material.) Hoffman suggests a dose of 1 to 2 ml of tincture three times a day.
Most herbalist agree that herbs are most effective when used together in well tailored formulations, so while Devil's Claw can be used on its own, you may get better results by consulting a herbalist.
See also: nutrimart's page of devils claw root