After rising from 300 elo to 700 elo in 3 months, my rapid rating starts to plateau.
I mainly play the London with white. With black, I play the Scandi/Caro against e4, and the Dutch against others. I play mostly 15|10 now when I have the time.
I tried hard not to blunder pieces to simple tactics, and find simple and forcing moves to attack, but my opponents just surprise me with some crazy moves and I have to defend. Basically, I will lose all of my games when I find myself in a defensive position.
Any recommendations (e.g. tips, learning resources) for me as a newbie? I feel frustrated with how dumb I am at chess and really want to get to 1000.
Read "My system" By nimzowitch and follow it. Furthermore, learn some basic pawn endings and try to repeat your opening lines like 100 times. Change Dutch with triangle system and Caro-Scandi with sicillian, London is okay.
Stop resigning is the first thing. In the past 30 days you've lost 76.5% of your games by resignation. You've only won 48.3% by resignation. Your opponent's are making you work for your win, do the same to them. One of the hardest things to do is win the won game.
Other than that, I like your opening choices, simple and adaptable. I'd suggest choosing just one against 1. e4 for now to be consistent and learn the plans of your opening, but scandi and caro are both great.
Middlegame play I'd say don't get too wrapped up in trying not to blunder. Sounds counterintuitive but it's going to happen, both to you and your opponent. You should be looking for their threats (checks, captures, attacks) but also make your own. You don't want to play the whole game on defence. If you do make a mistake, brush it off and play on! It's usually not the first mistake that kills you. In your most recent game, you might've survived down a knight, not down a knight and rook with an incoming checkmate attack.
Endgame, idk, you resign before you get that far. Keep playing, nobody knows endgames at 700. Just know a bit of your opening plans (don't worry about memorizing lines, you'll never get them until at least 1000) and look to create and attack weaknesses. Pawn breaks are key in the London and Caro-Kann. You can look into them if you're getting stuck on what to do in the middlegame.