My son (better at chess than I) was class C for much of 2nd grade, He broke out from only a few things.
- Chess.com tactics and CT Art 4.0 Tactics. Go up >50 points per week on chess.com. He went from 1600 to 2400 chess.com tactics in 4 months.
- Focus on opponents ideas more than his own
- Resist urge to trade out of impulse -- stop the trades that don't help. This could be as simple as he and his opponent have rooks facing each other on an open file, and he would just be impelled to capture. Then his opponent recaptures, seizing the open file. And then my kid has to work around it for many moves. For no reason. Impulse control.
- Stop trying to always find a great checkmating plan in middle game - just being up a pawn, then ganging up on another weak pawn, is enough to win - his coach would call this making realistic winning plans, and execute them.
https://web.archive.org/web/20140708101221/http://www.chesscafe.com/text/review780.pdf