All visa applicants are advised to apply for their visa as soon as travel to the United States is contemplated, and not later than 3-4 months in advance.
Overview-Visa Waiver Program
Please confirm whether or not you need to apply for a visa. You may not need to apply for a new U.S. visa if you already hold a valid U.S. visa of the classification appropriate to your purpose of travel, or hold a passport eligible for travel under the Visa Waiver Program, or if you hold a Canadian passport.
If you do need to apply for a nonimmigrant visa, please follow the steps below.
Note: If you are under 14 or over 79 years old, or if you previously received a U.S. visa that expired within the last 48 months and you are returning to the United States for the same purpose of travel, you may be able to obtain a visa without coming to the consulate for an interview Click here to learn how to apply using the Consulate's Drop-off Service.
How to Apply?
Please visit: http://www.ustraveldocs.com/ for details.