I wouldn't go too crazy with endgames, more than R+K and realising that you need to use your king as soon as the endgame is going to start.
When I was 1000 I almost never won or lost by just one pawn, the differences were bigger due to several blunders from both parts.
What Theoretical Endgames Should You Know as a 1000?
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Ladder checkmate, checkmate with queen, checkmate with rook, draw by repetition, draw by insufficient material, draw by stalemate and pawn push.