Start from reading and focus on sentence structure. Chat with people who are willing to correct you will be the best way to improve. Start with text chat to improve via reading, then move on to voice via conversing. Use simple and short sentence to start with.

Nyimalay, i think u shd need many practices. In my student life, i had done so many exercises for single pattern of basic grammer. After studying some amt of patterns, i had to do exercises on mix pattern of grammer. Do u hear that practice make perfect? After doing many exercises, u will know automatically what is wrong and what is right. It is very difficult to explain but it is real for studying English as a second language. U remember almost all the pattern of grammer. u wiil become expert after doing many, many exercise from various grammer text books, but two or three is seem to be enough. Don't be wavy. Emphasize on what shd u do. Ok.

if you wish, i can send you an e-book that could help....