How to rank up in 3 months

Hello, I'm looking to join a U1100 tournament in august for fun. How would I get from 400 to 1000 ish in 3 months?

Start taking some time before you play your moves to think about what your opponent is going to do.

Thank you. 
Any idea of how i can improve on that or is it literally just taking a second to stop and think?

Well, you have to be checking to see if you can figure out why your opponent made his or her last move and if your proposed move does anything positive or has left anything hanging.

In that same game, you had this position:

You were already up a rook. Why not take back with the queen? If your opponent trades queens, your rook advantage becomes much easier to convert to a win.

Instead, taking back with the pawn left your king all alone.

You have to think about such things.

Thank you for the tips. Much appreciated

Look for forcing moves like checks captures and threats, that's the best way to get to 800-900 rating

you can do this it's not that hard just play rapid more

Thank you !!

np you're welcome! saying this based on my experience I reached 1000 in a short time. You should just play as much as you can, that's how I did it but if you take some lessons and study openings it's gonna help you gain elo 2x faster. (I only knew the Wayward Queen Attack till 1000 💀🪦)

Don't listen to her, that's a terrible advice. Praticing is good, but it won't help without studying. Analyse your games without and with engine and think about what you were thinking at that time and what did I do wrong. Try to not hang pieces, look for forcing moves; 1. Checks 2. Captures 3. Threats (Attacks), and think what they achieves. Don't play checks randomly, it won't get you anywhere. Like the game @justbefair posted, 27. f4+ randomly losed a pawn and even hung a M1, think before playing a move for about 2-3 seconds; "Did I hung mate? Does this move loses material?" and check again and again until you're sure. And don't play Blitz and Bullet games before you can tink quick and good enough. That's all I could give, also solve puzzles and learn tactics. Solving puzzles helps to improve in lower levels a lot.

Wtf playing is the most important thing. No matter how much you try to learn by heart, it's not gonna be enough you need to play with high time controls and actually think that's what really matters

I followed just be fair's advice and did much better on my last game

That's defintely not much better, you shouldn't forget about stalemate and other kind of draws. Try learning Queen + King vs King and Rook + King vs King checkmates.

will do

And think more before moving, try to not hang pieces. At lower pieces, most of the losses are caused by hanging pieces and checkmates. If you can get over these, you'll get into 800 quickly.