Unless one takes serious interest in it and any thought of improvement is impractical and I have observed this lack of interest in many students developing into a phobia!
Some very good ways have been suggested for improving one's English grammar! I may also add that watching news channels and movie channels in English will also help get your pronunciations right and also improve grammar!
I agree with the author's suggestion of Wren & Martin when it comes to improve one's English Grammar and I too believe that there should be certain elements of practice and regular hard work on this which will really bear the fruit...