1. Get feedback
Ask one or two of your professors to examine your application and provide feedback. Do you have enough experience? Are your GRE scores too low? Seek information, especially, about your admissions essays.
2. Evaluate your admissions essays
Admissions essays are the trickiest parts of a graduate school application. Do yours answer the question or topic posed? Check the grammar, tone of voice, and content. Seek feedback from professors and successful applicants.
3. Rethink your recommendation letters
Did you choose the right faculty members to write letters of recommendation on your behalf? The faculty members you ask to write your letters must know something about you, have experiences that they can relate about you, think highly of you, and believe that you are well suited for graduate study. A lukewarm letter or one that provides few details will hurt your application. Reconsider your letters because a poor one can be the kiss of death to your application.
4. Get more experience in your field
Added experience in your field shows that you're interested, gives you something to write about in your admissions essay (and talk about in an interview), helps you determine if this is the field for you, and may improve your recommendation letters.
5. Take classes
Consider taking additional classes in your field or related fields. Or take classes in the graduate department to which you're applying. Most programs will let students take one or two classes as a non-matriculated student. This will help you learn, make contacts, and see if the program is right for you. Remember, however, that taking courses as a non-matriculated student does not mean that you will be accepted into the program - you still have to apply like any other student.