What is the most important thing you did to improve in chess?

My game improved significantly when I put together an opening repertoire based on database statistics from masters's games.  Also when I started putting attention to the importance of piece activity, dynamics, and strong openings knowledge

Chess videos from titled players have helped a lot also, specially videos from Simon Williams, Dennis Monokroussos, Jonh watson, Sam Shankland, Rafael Leitao. David Vigorito, Nadya Kosintseva, Daniel King, Jan Gutafsson, Victor Bologan, amongst some others.  I have a chess video collection of about 150 hours, plus membership in chess video websites. 

Being around other chess players who want to improve their game helps me.  

And when I was (much) younger I hated losing more than I do now.  When you hate losing it motivates you to learn and improve more and faster.  At least it did me.  

My chess skills took a quantum leap after reading chess Informants. I had a peek inside a GMs brain. I could evaluate positions, weaknesses better. And material imbalances. And trying to solve ECC puzzles help my tactical vision.

I think one of the keys of improvement is to learn constantly in a systematic and efficient way. 

I do this already with openings and tactics, and also with endgames (basic knowledge) in Chessable.

What I still need is to make a list of my common mistakes. I am sure that working systematically on my mistakes will bring me at least 200 rating points in one year, perhaps even more. 

I am planing to do all new lessons in chess.com, starting with the intermediate level. These lessons are terrific, and I am sure they will help me to improve my game. The idea of making an interactive video is really great.

birds opening https://youtu.be/-AdSN6CpuWQ

Brilliant thread for a struggling novice like me. Many Thanks.

It is what I am playing, the French. I like it.

Many years ago, I made the breakthrough from about 1800 to 2000 (OTB rating) after I started teaching chess tactics and strategy at a local chess club. It seems that the need to break the game down into bite-sized elements (for teaching purposes) clarified my own understanding of the game.

I experienced a similar thing with tennis. I got better in tennis because I tried to understand better the technique. I also give chess lessons, but only for beginners or rather weak players, and only have one hour per week.

Over the last 10 years on chess.com forums, from time to time, I've taken as long as an hour to answer posts of new-ish players who post a game asking for advice. Often they're grateful and send me a thank you message, but as you guys are saying, the one trying to teach benefits too.

I should do the same. However, by far the most important thing I should do this year is to "teach myself": go through my games as I would analyze the games of somebody else, make a list of the common mistakes, put the most relevant things on flash cards and begin to learn all this stuff. 

tactics-brought me to 1800 (these really makes the big difference)

opening preparation brought me to 2000. (lines im comfortble in middlegame)

I did a go with tactics in the last 6 months, and this of course helped me a lot. Not only that I can see faster how to win material with tactics, but I can prevent my opponents to win something with tactics.  In the last time I did more openings (trying to fill the gap in my black rep against 1.e4), but soon I will go on with tactics again. My biggest problem is still everything coming after 1.d4 with black. I have a terrific book covering all this stuff, but it is a lot to be learned. There I have to play according to opening principles, which is not enough against strong players.

I joined a chess club and started playing against real live human beings.

You can play all the online chess you want, but there is no substitution to sitting down at a board with at least 45 mins each on the clock and just immerse yourself in the game.

Not only does it make me better, I enjoy it much more than sitting alone behind a computer screen for hours on end.

Also, make friends who play chess. Analyse each others games, try things out, talk about stuff you've learned, questions you have.

And stop playing blitz or bullet.

Since long I am planing to join a club. I always have some stupid excuses like "I would like to fill my gaps in the opening" or "do I really want to commit to play chess once in the week? What if I want to play tennis in this day?"  Nonsense, I know. I think the great thing about playing in a club is to have the free lessons from stronger people who crushed you. And you can measure yourself with other people. Definitely the right thing to do in 2019: join a club and get better OTB.

How long are already playing in a club? Did you see already some improvement? 

Interesting. I am forever planing to join a club as well, but I always have an excuse, like, just when I reach 1500 I'll join, otherwise I'll be crushed and just waste time. 

I stated playing chess one year ago and what helped most to improve my game is doing tactics everyday, I try to learn about 5 to 10 new tactics a day and review about 20 - 30 tactics. 

Think of it this way: are you about to quit chess?

If so, then sure, get as prepared as possible, then play in 1 or 2 tournaments and quit

But if your goal is to improve, it doesn't matter if you're "not ready" to join a club and play. Just go play. A year later you'll have improved a lot, and that's the point of going.