I know a guy who speaks primarily Yiddish and a broken, chassidishe English wanting to learn to speak/read/write English properly for business purposes. How would you recommend he go about it?
1. Speaking: Force himself to speak only English to whomever will listen to him. He should persevere no matter how broken he sounds. Grocery stores, restaurants, dry cleaners, gyms, neighborhood children, random people on the street to ask a question or direction, etc.
He will very quickly find that he is able to get the gist of speaking, but is lacking vocabulary. He can pick up a grammar book for English as a Second Language for verb tenses at a library.
2. Reading: Start by reading childrens' books, underlining each word he does not know and translating that word above the English. Book after book he will find that there will be less and less underlining. Toddler and young childrens' books have two-four sentences per page. Reading will fill in the everyday vocabulary.
Next stage would be to read the periodical which he would want to read if he were to know English. (dictionary in hand) That is where he would pick up the business/professional vocabulary.
3. Writing: After he finishes a page of reading a children's book a few times, he can summarize it or just write what he read and then compare. He will quickly be able to fill in the missing words after he does this just a few times. Rewriting a story (even if it only a kid's book) will give him the flow of the language.