@Consept here's how I did it 
I started watching remote chess academy when I was rated 700. I looked at video lessons like the secrets of strong players. The older lessons on youtube are what I found helpful for reaching 1600. This was combined with starting a lichess.org account and analyzing every game with a computer. I made many studies on my opening repertoire. I combined my own understanding with the computer calculation to figure out my opening play. I find that I retain more when I build my own opening rather than copy someone else.
Along with that I studied many paid courses from remote chess academy and improve my chess. I found the most helpful course to be the grandmasters opening laboratory 2. It taught me techniques that applied against Master level players and shows how to make a positional sacrifice from the opening.
I practiced theoretical endgames with a chess encyclopedia and a computer. This helped me to find draws in otherwise lost positions.
Most of my mistakes happen in the middlegame. This is either due to misunderstanding the optimal strategy or by miscalculation. There are courses that might help but after a while I got diminishing returns from courses.
Before my tournament games I looked in a mirror and started repeating affirmations. I visualized myself becoming a grandmaster and playing a beautiful game against strong opponents. This is how I ultimately beat a national master.
Some good channels include John Bartholomew and chessnetwork.