This one is a little bit tricker, because the raptors are... well... fast. I recommend the using of the shotgun. It can kill a raptor with a single shot if the raptor is close enoguh.
All you need to do is to kill the raptor before it bite you. If the raptor touch Lara and the life bar appears, you failed. Try again.
You need to finish the two final levels, "Lost Valley" and "Tomb of Qualopec" without a single bite. If you succeed, the achivement should pop just after Lara kicks Larson in the face.