There is a lot you can learn on your own. You can start by taking a look at a Grammar book and looking for free material online, so you can, not only read, but listen to it as well. It will be very hard, though. VERY hard. But feasible.
I highly recommend getting help from somebody - preferably a real teacher. If you are a teacher yourself, maybe you will have an idea how to proceed and you might get an English native speaker help you - with your guidance as a teacher. Still VERY hard. But feasible.
If you decide to spend a little money - VERY little, really - and take just one class with a good teacher, you will experience the difference. I dare you! Take just one class with one of the many good teachers you can find here. Don't be afraid to spend that little bit of money that will show you how to get started. And enjoy the experience.