Chess notation cheat-sheet (for new readers)
Pieces: K king · Q queen · R rook · B bishop · N knight · (a pawn move has no letter)
Actions: x takes · + check · # mate · O-O short castles · O-O-O long castles · e8=Q pawn promotes to queen
Annotations: ! good move · !! brilliant · ? mistake · ?? blunder
Spotting the Elephant Trap and Rubinstein queen-traps before you grab the pawn
Two of these traps share one trigger: a knight reaches d5 and someone reaches for a pawn that is not really free. The Elephant Trap springs after 3.Nc3 Nf6 4.Bg5 Nbd7 5.cxd5 exd5 6.Nxd5? (White's knight grabs the d5 pawn) Nxd5! 7.Bxd8 Bb4+ (Black's bishop checks from b4) 8.Qd2 Bxd2+ 9.Kxd2 Kxd8, where the bishop check forks the king and the bishop sitting on d8 and Black emerges a clean piece up. In the trainer you get the board one move before 6.Nxd5?, so the job is to see that the d5 pawn is poisoned and find the refutation, not to memorize the moves.
The Rubinstein Trap is the same idea pointed the other way. After 1.d4 d5 2.c4 e6 3.Nc3 Nf6 4.Bg5 Be7 5.e3 0-0 6.Nf3 Nbd7 7.Rc1 c6 8.Bd3 dxc4 (Black's d-pawn captures the c4 pawn) 9.Bxc4 Nd5 10.Bxe7 Qxe7 11.Ne4 the threat 12.Nd6 (White's knight jumps to d6, forking the queen and rook on the c-file) hangs over the position, and a careless Black move drops the exchange. Read it as a cue: when a knight eyes d5 or d6 and your back-rank pieces are tangled, check for the trap before you move. For the full account of who fell for what, the guide linked below carries it.
Minority-attack tactics in Queen's Gambit Declined chess puzzles built on the Carlsbad c6 weakness
The Exchange Variation, 4.cxd5 exd5 (White's c-pawn trades for Black's e-pawn, leaving a symmetrical d5 vs d4 center), builds the Carlsbad pawn structure, and the tactics there cluster around one target. White pushes b4-b5 and trades bxc6 to leave Black with a weak pawn on c6, then the shots arrive: knight forks that hit the loose pawn, pins down the half-open c-file, and discovered hits once the rooks double. These queen's gambit declined chess puzzles drop you into those positions at the moment the combination is on, so the minority attack turns from a plan you nod at into a sequence you calculate to the end.
At the board, the cue is quick to rehearse. Find the weakest pawn in the Carlsbad, usually c6 for Black, then count the attackers and defenders on it and look for the in-between move that wins the count. The set also hands you the defensive side: kingside counterplay or pressure on the e-file that flips the initiative back, so you train to hold the c6 pawn as well as to win it.
Queen's Gambit Declined chess puzzles: the Cambridge Springs ...Qa5 win and the Bxh7+ Greek gift
The Cambridge Springs hangs on 6...Qa5 (Black's queen swings to a5). The queen steps off the h4-d8 diagonal to unpin the f6 knight, pins the c3 knight to the e1 king, and sets up ...Bb4 (Black's bishop drops to b4, pinning the knight a second time) and ...Ne4. The payoff to drill is the ...dxc4 in-between move: when White answers with a loose Bd3, ...dxc4 collects a piece before the trades finish. The puzzle hands you the position right as White slips, and you have to spot that the c3 knight is overloaded and cash in.
The flip side is White attacking. When White lands a bishop on d3 aimed at a castled Black king with the f6 knight gone or pinned, the Greek gift Bxh7+ (White's bishop sacrifices on h7 with check) Kxh7 Ng5+ followed by Qh5 can break through, a Pillsbury-style assault. The thing to check before sacrificing is concrete: is h7 defended only by the king, can the knight reach g5 with tempo, and does the queen get to h5 or h7 in time. These positions appear from both sides, so you practice firing the sacrifice and refuting it.