You should apply for your visa appointment as soon as you receive your Form I-20 or DS-2019. The consulate or embassy may take longer than you had planned to issue your visa, or may require you to obtain additional documents — so plan ahead! You may want to contact the consulate or embassy ahead of time to inquire about the details of their visa application procedure. Questions you might ask include:

What is the current waiting time to get an appointment?
What documents are required?
How long will it take to receive my visa?
Is there a processing fee?

It is strongly recommended that you review the instructions for how to apply for a visa on the website of the US embassy or consulate where you will apply.