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! 
A very common pattern around 1500 level is that players improve tactically much faster than strategically.
They calculate reasonably well, but still feel uncomfortable in positions where there is no immediate tactic.
In my experience, a lot of improvement comes from learning to evaluate positions more calmly:
• Which side has more space?
• Which pawn breaks matter?
• Which piece is misplaced?
• Which endgames are favorable?
Strong chess is often less about finding brilliant moves and more about understanding the position a little better move after move.
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.