Tactics
The absolute pin
When the piece behind the pinned one is the king, the pinned piece cannot legally move at all. That is not a matter of judgement, it is the rules, and it makes everything the pinned piece was doing stop being true: it defends nothing, it blocks nothing it could not be pushed off, and it can be attacked at leisure.
How to spot it
Find the enemy king, then look along the lines running through it. Anything of theirs on one of those lines with one of your sliders at the far end is frozen. The standard follow-up is to attack it again with something small, a pawn, and win it for nothing, because it cannot run.
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. White to play Play it out →Answer
24.Nxe6+ Kf6 25.Nxf8
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2. White to play Play it out →Answer
23.Rxe8+ Rf8 24.Rxf8#
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3. White to play Play it out →Answer
38.Qxe6+ Rf7 39.Rd8+
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4. Black to play Play it out →Answer
34...Rg2+ 35.Kh1 Rxf1#
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5. Black to play Play it out →Answer
17...Nxf3+ 18.Qxf3 Qc5+ 19.Qf2 Qxc4
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6. White to play Play it out →Answer
21.Nh7+ Kg8 22.Nxf6+ Qxf6 23.Rxf6
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7. White to play Play it out →Answer
32.Qxg7+ Rxg7 33.Re8+ Rxe8 34.dxe8=Q#
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8. White to play Play it out →Answer
34.Rxh7+ Kxh7 35.Qh4#
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9. White to play Play it out →Answer
24.Nf6+ Kh8 25.Rh5#
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10. Black to play Play it out →Answer
17...Bxe3 18.fxe3 Qxe3+
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11. White to play Play it out →Answer
34.c6+ Kd6 35.Rd1+ Kxc6 36.Rc1+
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12. White to play Play it out →Answer
31.Ng5+ Rxg5 32.Qxf7+ Kh8 33.Rxf2
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.