As already mentioned, online courses would most likely be your best bet. I don't know if they'll include some of the phrases or the specific things that you're looking for. I must say, your English is quite fine!

Another thing that may be beneficial is reading books. I know, it sounds rather silly, however it's a great way to increase your vocabulary and understand a language better. When you hit a word that you don't understand, stop and look it up; don't just skim over it. Once you know what a word means, you'll seem to notice it more often.