Advice for further study

1.   Read in English as much as possible.  

But don't start with something too difficult.  You can't make any progress if it's too difficult.

Find something that is interesting and easy for you, whatever level that happens to be.

Work through step by step, level by level, and you will improve eventually.

2.  Study grammar regularly.  I recommend English Grammar in Use  book series.  Start at the first lesson and work your way through all the exercises.  It's guaranteed to improve your English accuracy.

3.  Continue studying in a class.