You can increase your admission chance if you know what factors are important in getting a admission. Here is the list of those elements which are very important for getting a admission:

1. GPA

If you are still in school try to increase your GPA as much as you can. Even if you have left the school, you can upgrade your GPA by taking some more extra courses.

2. Publications

Publications are one of the most important factors. Note that journal papers are much more better than conference paper. However, they are harder to write and getting accepted. Try to submit your publications to more prestigious  journals and conferences. Remember to also put your submitted papers in your resume.

3. Find a professor who agrees to work with you.

Try to contact profs who you like to work with. Send them an email with your resume and research interest and express your desire to work under their supervision. However, they usually receive a lot of spam emails plus similar requests everyday. Thus, it is possible that they don't read your email and you get no reply. Therefore, if possible try to meet them and talk with them face to face. In a meeting they can easier evaluate you and they will know that you are very determined.

If a professor accepts to get you for his\her research group, you have a high chance to get accepted.

4. Scholarships and awards

Having won more scholarships and awards shows that you have been a more successful student. Therefore, apply for any scholarship and award contest you can during your undergrad.

5. Recommendations,  SOP  and resume

Spend enough time on your SOP and resume to make sure they look good and professional. Also, you must provide 2 or 3 recommendation for each school. Therefore, try to make couple of profs know you as a hardworking and smart student. Try to do your assignments and projects at highest level and even try to do some extra projects.