I am an intermediate learner, having been studying for a little over a year. I study around 2-3 hours a day, 4-5 days a week. I listen to the radio every day and watch TV in Thai. I read the newspaper too and learn 40-50 new words a week. I haven't been doing this consistently for the entire time, sometimes it has been a lot less.

I am fairly satisfied with my progress in this period but cannot help but think that if I had a job working around Thai people or volunteered with Thai people, my progress would be quicker. I practice with a teacher and also with my Thai girlfriend. For foreigners who have an advanced level of Thai, how has working with Thai people helped? I don't work here but think it might be helpful for me to find volunteer opportunities, maybe working with kids or elderly people, in order to improve.

I'm not sure, taking into account the amount if study you've done compared to me, whether you'd consider my Thai advanced. However in answer to your question:

I've been living and teaching English in Isaan for the past 3 years. As part of my job I try to not speak Thai when I'm teaching, although often use it when I want to speed things up a little and if I need to convey important information to the students.

I only occasionally speak with my co-workers in Thai, as they're mostly Thai English teachers, although we sometimes jump around between languages in a conversation as they might not know the English word. Almost all conversations with the admin staff are in Thai though, as they don't speak English.

I think that it has definitely improved my Thai, even though I have done very little self study in the past 2 years. But if I want to say something, and I don't know the words, I'll look it up in the talking dictionary on my phone and then put it into a sentence. The same words are then regularly used during my time at the school. Although if I was doing more active self study, I'd have had a much greater vocabulary to use lol)

Also during class I'll teach various topics, usually I'll start by drawing or putting up a laminated picture on the whiteboard. The students natural reaction is then to say the word, usually in Thai or Isaan, since they don't know the English word yet. They often do the same when I'm testing them if they don't know the answer. As a result, I unwittingly, without even trying, pickup the Thai or Isaan words for different things (often some of the more uncommon words lol, as the common ones they know the English for already).

But in general the greatest thing which I think I've learnt is to be confident with my Thai, as I often need to try and explain things to a class of 30-40 students lol. Which also means I need to speak relatively clearly, otherwise I'd look like an idiot if I'm not saying something correctly (If this happens the students will usually help me to say the word properly, at least to an understandable level lol, tones I sometimes make attempts at them when I know the tone, but usually I put them in the "too much effort, too difficult, people can work it out easily enough based on the context" basket lol.

Anywho I hope that sharing my experience has helped. I would definitely recommend doing a bit of teaching, but do it because you want to teach, it's subsequent effects on your Thai are just a bonus. In general though any interaction with Thai people will help you to learn more Thai and to learn how words are best used in conversations. I find these days that I often learn new words just from listening to my gf talking to her friends or when random crazy people approach me in the street lol. I'll then ask my gf to confirm the meaning afterwards, to ensure I've got the general jist of things correct.

Currently working in Thailand. All my coworkers speak English better than I speak Thai, so job doesn't help.

I have a few Thai friends who can't speak English, that helps.

When I was in Europe, I used camfrog for online chat, that helped a lot because my problems is listening, and on camfrog I can read and write which is much easier to understand for me.

Being in a work environment didn't help my vocabulary because everything was conducted in English, but listening to co-workers speaking to each other outside of work helped my pronunciation. You'll need to surround yourself with non English speakers if you want to progress faster.