Med schools weigh your pre-med GPA more heavily than your overall GPA. Your pre-med GPA should be at least a 3.0 (on a 4.0 scale). Your pre-med courses should include two semesters plus labs in general biology, general chemistry, physics and organic chemistry. Additional required classes may include microbiology, biochemistry and calculus. Your pre-med GPA is the most important factor for getting into medical school. If any grades are lower than a C (2.0), retake the course and address the issue in your personal statement.
Another critical measure of your ability to succeed in med school is the Medical College Admission Tests. The MCATs are standardized exams, largely based on material taught in pre-med classes. The exam is divided into three sections: biology and organic chemistry, chemistry and physics, and reading comprehension with a timed essay. Students routinely spend three months preparing for it. The Association of American Medical College, which administers the MCATs, posts online practice exams. Take a few practice tests and compare your scores to your med school's minimum and average MCAT scores, also posted on the AAMC website. Don't give up if you fall short. Hit the books and consider taking a commercial MCAT study class.
The personal statement is a two-page essay within the AMCAS application. The key is to express your reasons for wanting to practice medicine and the strengths you can bring to the medical community. Avoid sounding too general ("I want to help people") or obvious ("I am a good student"). Relate your personal experiences, concerns and desires to illustrate your motivation and values. Don't simply list your abilities. Use real-life experiences to demonstrate your traits and strengths, such how you overcame an obstacle or grew from a challenge. Draft a statement early, ask mentors for feedback and plan to rewrite it a few times.