Do you use correct English as often as possible?
Have you tried learning from dialogs? Learning new expressions by heart is the only thing I could think of to be really fast.
I tried learning from dialogs in my quest to learn conversational English fast.
I had a job(in a call center) by just doing so for 3 months. I read conversations again and again till I get to say them automatically. But of course, you need to put those newly learned expressions into practice, so you may do a self-talk or a chat with a friend which is much better. I still do copy fixed expressions from other people, just like what we do with collocations. It's quick learning and sure to be accurate expressions. It worked for me, it may do well with you.