Maintaining good flexibility around the ankle, particularly the Achilles tendon and calf muscles, is probably the best way to prevent plantar fasciitis.
Donley BG, Moore T, Sferra J, Gozdanovic J, Smith R. The efficacy of oral nonsteroidal anti-inflammatory medication (NSAID) in teh treatment of plantar fasciitis: a randomized, prospective, placebo-controlled study. Foot Ankle Int. 2007;28:20-23.
Pasquina PF, Foster LS. Plantar fascitis. In: Frontera WR, Silver JK, eds. Essentials of Physical Medicine and Rehabilitation. 2nd ed. Philadelphia, Pa: Saunders Elsevier;2008:chap 86.