Tactics
The skewer
A skewer attacks a valuable piece through to something behind it. The front piece moves, because it has to or because it wants to, and you take what was behind. It is the pin turned around, and it is more forcing than a pin, because the piece being attacked first is the one that cannot afford to stay.
How to spot it
Look for an enemy king or queen with a rook or bishop of theirs directly behind it on a line you can occupy. Checks are the natural skewer: the king must move, and whatever was standing behind it is yours. Endgames are full of these, which is why the same trick decides so many rook endings.
The positions
Easiest first. Every one is from a real game, and the rating under each board is what it costs the players who have tried it on lichess.
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1. Black to play Play it out →Answer
37...Rh1+ 38.Kf2 Rxa1
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2. Black to play Play it out →Answer
31...Rh1+ 32.Kf2 Rxc1
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3. White to play Play it out →Answer
20.Bb5 Qc7 21.Bxe8
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4. Black to play Play it out →Answer
32...Ra1+ 33.Ke2 Rxg1
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5. White to play Play it out →Answer
17.Bf4 Qe6 18.Bxb8
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6. Black to play Play it out →Answer
38...Qh1+ 39.Kf2 Rh2 40.Rxh2 Qxh2+ 41.Kf1 Qxb2
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7. Black to play Play it out →Answer
20...Rdg8+ 21.Kf3 Rh3+ 22.Ke2 Rg2+ 23.Rf2 Rxf2+ 24.Kxf2 Rh2+ 25.Kf3 Rxc2
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8. Black to play Play it out →Answer
24...Rd8 25.Qxb6 Rxd1+ 26.Kf2 cxb6
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9. Black to play Play it out →Answer
32...Rh8 33.Qxg3 Qh1+ 34.Kf2 Qxd1
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10. Black to play Play it out →Answer
35...Rxf4+ 36.Kxf4 Bh6+ 37.Kg4 Bxc1
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11. Black to play Play it out →Answer
39...Re8 40.g5 Rh8+ 41.Kg4 Rxh1
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12. White to play Play it out →Answer
37.Rd7+ Ke4 38.Re1+ Kf3 39.Rxe8
Reading about a pattern is the easy half. Motify finds the positions where you missed one, by running your own lichess and Chess.com games through Stockfish, and puts each of them behind two or three puzzles on the same idea so you meet it having just found it three times. See how Motify works.
Positions from the lichess puzzle database, released under CC0.