The standard GPA needed for acceptance to most graduate schools is a 3.0. Many other schools will accept students with less than a 3.0, though, so don't rule out graduate school if your GPA is below that mark. Concentrate on and market your strengths. If your GPA is below the average of those generally accepted, work on enhancing your personal statement, admission test scores or gain some relevant work experience. The types of courses taken, your GPA and evidence of improvement, if you did not start out strongly, will all be looked at.
Some programs require a specific major or courses to be admitted.
Letters should be requested early from either professors or employers who can attest to your abilities. Individuals who can speak most clearly about your abilities and accomplishments are your best bets. Admissions officers like to see specific examples about different facets of the applicant. The reference should include some statements about your skills, accomplishments and character. They can also be used to explain a negative in your application.