Ask teachers in person in May or June of Junior year
One recommendation must be from a core subject teacher (math, science, history, science, or foreign language); second recommendation from any subject teacher
Request must be sent through Naviance: ("College" tab; "Apply to College">Letters of Recommendation; click blue ADD REQUEST button on the right, select teacher from drop down menu and click/check circle "all current and future colleges I add to my Colleges I'm Applying To list; add a personal thank you note; click blue SUBMIT REQUEST button on the bottom right).
The Common Application is a universal college application that applicants may use to apply to 900+member colleges and universities. Many colleges begin accepting applications in August. Work on your application during the summer at www.commonapp.org