In our opinion, input is the most important way to learn English. In his book, "The Input Hypothesis: Issues and Implications", Stephen Krashen cites a fascinating example (originally described in Adrian Fourcin's 1975 article "Visual feedback and the acquisition of intonation"), which shows that it may be possible to learn great output skills by input alone (without producing any output).
Richard Boydell was a disabled child who couldn't speak or write (most of his body was paralyzed). He was intelligent and he could understand other people. When he was 30 years old, he got a special typewriter. He could type on the typewriter with his feet. In this way, he could communicate with others.
Here is what he wrote:
I acquired an understanding of language by listening to those around me. Later, thanks to my mother's tireless, patient work I began learning to read and so became familiar with written as well as spoken language. As my interest developed, particularly in the field of science, I read books and listened to educational programs on radio and, later, television which were at a level that was normal, or sometimes rather above, for my age. Also when people visited us ... I enjoyed listening to the conversation even though I could only play a passive role and could not take an active part in any discussion ... As well as reading books and listening to radio and television .... I read the newspaper every day to keep in touch with current events. (from Fourcin's article, cited in Krashen's book)
As you can see, Richard Boydell's writing was excellent, although he had never written anything before. He could use advanced grammar and vocabulary, because he had been reading books, newspapers, listening to the radio and people's conversations. It seems that input — and nothing more — gave him good English.