The best thing you can do is live there. This may seem like a typical answer, but it isn't. I learned Polish on my own and thought I knew it well until I went there. I could not understand anyone. I had to talk to people for many months to get to the point where I could communicate. It was not like that when I learned other languages. Polish is tough, and you need to respect that. I would never have become as good as I am without actually living in the country and working there for a few years. I am still nowhere near perfect, but being in the country really helped a lot. That is my best advice for you. By the way, I also study Russian, and I think I will have to either live there or make good friends with Russians to learn it well. Good luck!