Enrolling in adult training class is the most efficient way for adults to learn English at present, because self-study may lead to many misunderstandings, and they may gradually "let themselves drift" without supervision and reminder.

So in general, the most efficient and time-saving thing is to report to class. Moreover, oral English learning needs constant speaking and practice in order to have good results. Usually, private practice may not have a good English environment. Therefore, it is necessary to sign up for adult oral English training classes and have someone practice speaking English at any time.