Secure a private tutor whose specialty is GRE preparation. Do this at least a month before your test date. You can find a tutor through your local college or university.
Complete practice quantitative and verbal exercises in your preparation book. Time the exercises so you are used to working under the pressure of a time limit. When finished with each exercise check your answers.
Make flashcards for questions or concepts that you continually miss on your practice exercises. Review these daily until you understand the concepts you are missing.
Set the timer for 30 minutes and practice writing the essays that will be required on the GRE. You will have to write two essays and will have 30 minutes for each essay. Practice prompts are available in your preparation book.