Thought I'd write down a few tips that I found useful in moving my game from 800 to 1200. I do not claim any special ability or insight, this is just what worked for me. Perhaps they will be useful for others.
1) You want longer time-controls! Yes, bullet chess looks impressive, but give yourself time to think. I suggest 15+15. I estimate moving from bullet to classical added 150-200 points to my rating.
2) Use the 'analysis' board after each match. You have a God-level chess player at your beck-and-call, who will analyse your game at any time of the day or night. Take advantage of that. Take a look at your worst blunders, and try to understand *why* it was a blunder.
3) Ignore 'inaccuracies'. At this level, they are irrelevant. Even 'mistakes' are not that important, given your rating. It's really just your blunders that you want to focus on. Aim to reduce your blunder count to zero.
4) When playing white, choose one opening, and stick to it. You'll rapidly learn how to play the first few moves very well. Like most things, it's (almost) impossible to win in the early stages, but it's certainly possible to lose it. Other openings can wait till later.
5) 1. e4
6) Have a plan or aim for each move. Honestly, when I started I thought 'that sounds like good advice, but surely *every* move can't be attacking or defending? Surely some are preparatory moves?'. However, it's true. Now 99.9% of my moves have some specific aim.
and after doing all that, I started winning, and was shocked how fast I improved. Now, how to get to 1500??