SAT, could you please advise me on how to improvement my score upto 1550+.

Focusing on the topics that you either don't know so well or keep making careless mistakes really helps. Make sure you go over every single topic- especially the ones that frequently appear on the SATs. See why you are getting questions wrong and analyze why you chose an incorrect answer- what was your reasoning behind it? Finally, try taking practice tests again and again until you get a perfect score. 

Good Luck!

Thank you so much for the advice but could you also recommend me a book for practice tests...I have done all provided by college board