How to go from an 1800 player to a 2000 player?

Assuming you have what it takes, I’ll tell you a few things that worked for me.

Opening Theory -

I used to work on a particular opening against my program playing the opposite color. So if I wanted to learn e4 openings, I’d actually let the computer play white and try different defenses as black. The idea was to see what some of the stronger lines are and become familiar with the general theme of the opening and learn to avoid opening traps. It’s not about memorizing the entire opening book but to know the pitfalls of straying from the book and why certain moves are weaker than others and how to gain an advantage when your opponent strays from a stronger line.

Then I’d play online (mostly blitz) against similarly ranked players (+/- 150) as white playing e4 and try the same lines my program was playing against me and try to gain an advantage out of the opening.

It’s important to not think about rating and to play people both stronger and weaker. You’re not learning anything if you’re losing all the time to much stronger players. It hurts your confidence even. Beating weaker players helps reinforce your chess technique. It’s very important to be able to close in a winning position.

Make sure you know at least one opening well with white (e4 or d4 - ideally both) and two defenses well with the black pieces (against e4 and d4).

If you ever come across some unotherdox openings that cause you trouble, just play those against your program and you will see what the stronger lines against that opening are. The real goal of opening theory is to help you come out of the opening with a slight advantage or at least at parity.

Middle Game -

Tactics training at the appropriate level definitely helps but something that helped me a lot were videos in which GMs or IMs analyze their own games. It helps you understand the way they think and the way they analyze a position. I found the videos by Josh Waitzkin in the Chessmaster series very useful. They really helped me understand some advanced concepts. It’s also good to analyze your own games. Most programs allow you to do this and it really helps if you know what the best sequence of moves at certain points is cause although no two games are the same, you will end up with similar positions a lot of the time and it helps to know the best line of attack/defense.

Endgame -

Do the usual endgame drills. Rook and pawn endgames are probably the most important along with king and pawn endings. You should know how to get mate with two bishops or with a bishop and knight or even with a queen against a minor piece. Practice these against your program. End game calculations need to be very precise and this is where practice makes perfect.

There is no magical formula to getting to 2000+. It’s a combination of natural talent and hard work.

Above all, have fun when you’re playing and don’t take a loss too personally and look to learn from it.