Play a lot, analyze your games, and primarily study tactics. Your knowledge of openings, endgame, middlegame, etc. will come from analyzing your games and going over grandmaster games. Only study one of those specific topics if it is clear you are specifically losing because of that topic.
Source: https://www.gautamnarula.com/how-to-get-good-at-chess-fast/
As a coach, I can help you with any part of that process. Good luck! 
I'm stuck at 1500 rating for quite a while now, whenever i try to increase my rating i end up decreasing it. So, can anyone tell what do I have to do to reach 1600 and further.