Although your GPA and GRE score are the two most important factors in the selection process, other factors play an important role: complementary fields of interest, fluency in a foreign language, creativity, commitment, personal motivation, and character. Personal characteristics are important if you are applying for a TA position. Even if you do not have the highest GPA + GRE, you may fit well within the graduate department.
Other factors that may play in your favor include regional diversity, a well-written resume, strong letters of recommendation, a strong personal statement (definitely have your academic advisor look at it), a good writing sample, pre-professional job experience, volunteer work, research experience, publications, and presentations. You may also be invited to group or personal interviews.