You start as soon as possible. Your preparation includes test such as SSAT, TOEFL, application process, interviews. These are a lot of works especially if you aim to apply to schools with excellent reputation and to several schools. Summer will be most important to prepare. Please do your best with test prep and get all application information, and start to write and fill application form. As you begin, you will know how much and how long it would take. Therefore, PLEASE HURRY UP!。