Ask HN: What's the best way for a foreigner to improve English to a great level?

Talk to yourself (in your head or out loud, whatever floats your boat) and think in English. Do this constantly when you're walking alone, doing the dishes, folding laundry, etc. It's a good way to practice and get yourself used to not having to rely on your mother tongue during downtime when you cannot do focused study/practice.

The first thing to do is to always be listening to people speaking English. Try to be aware of how they pronounce things and compare them to how you do it. Be aware of little things like verb conjugations. People will still understand you if you do it wrong but you'll definitely stand out as a foreigner. Also, don't talk too fast.

In your case this won't work, but try to stay away from other speakers of your native language. I see students at UC Berkeley who end up getting roommates from their same country. This is a very bad idea because they won't be forced to adapt their brain to the new language. I always found that having a girlfriend who speaks the language I'm trying to learn was a good idea.

Reading books will help your vocabulary but it probably won't help your understanding of spoken language. What I did when I was living in a foreign country trying to learn the language was to watch children's TV shows. Once I was able to speak and understand at a 5 year old's level I felt like I was ready to expand my horizons.

If you have friends or coworkers who are native speakers, ask them to please correct you when you say something that isn't perfectly fluent.

Otherwise most people will ignore your mistakes, rather than risk insulting you.

I'd recommend taking an intensive ESL course, which you presumably have many options for at local universities. (My wife, who is Japanese, is similarly looking into options.)

If that isn't an option:

For listening comprehension, and eventually speaking, practice "shadowing." Have her listen to interest-appropriate TV shows and say exactly what the speaker is saying, in real time. (You can also do this exercise with transcription.) It will be maddeningly difficult at first, but with literally hours a day of doing it, she will see radical gains.

This is a large part of the training for professional translators/interpreters. In my experience it works very well. It is also some of the most frustrating work I've ever done.

Read books out loud. My English, both speech and vocabulary, improved dramatically after I spent weeks sitting outside on the balcony reading Lord of the Rings out loud to myself.