The most common mistake I see is then people plant their foot WAY in front of their bodies and come down on their heels. Your foot should make contact directly beneath your center of gravity or maybe slightly in front of it, with most of the impact happening mid-foot.
(Source: theinnerstrength)
Top of the Hub, Boston (Taken with picplz.)
(Taken with picplz in Trabuco, CA.)
(Taken with picplz in Boston, MA.)