Tactics
The advanced pawn
A pawn two squares from promoting changes what everything else on the board is worth. Pieces have to stay home to watch it, defenders become deflectable, and sacrifices that would be absurd anywhere else work because the pawn arrives as a queen.
How to spot it
When you have a passed pawn on the sixth or seventh, look at what is stopping it and ask what would remove that piece rather than how to protect the pawn. A rook given up to clear the promotion square is a fair trade, since what you get back is a queen.
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
46.d8=N#
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2. White to play Play it out →Answer
57.Be6+ Kb7 58.c8=Q#
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3. Black to play Play it out →Answer
21...e2+ 22.Ke1 Qg3#
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4. White to play Play it out →Answer
53.e8=N+ Kc6 54.Rc7#
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5. White to play Play it out →Answer
37.Rc8+ Nxc8 38.e8=Q+ Rf8 39.Qxa4
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6. White to play Play it out →Answer
45.b8=N+ Kb6 46.Rxf1
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7. Black to play Play it out →Answer
28...Qxf3 29.Qxd6 h3 30.Qg3 hxg2+
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8. Black to play Play it out →Answer
40...Bxa1 41.Nxa3 Bc3+ 42.Kxc3 a1=Q+
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9. Black to play Play it out →Answer
18...Rxd1+ 19.Kxd1 a2
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10. White to play Play it out →Answer
25.Rf7 Qxf7 26.exf7+
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11. White to play Play it out →Answer
51.gxf6 Kxc5 52.f7
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12. Black to play Play it out →Answer
43...b3 44.Rxc1 axb2 45.Rb1 bxa2 46.Rxb2 a1=Q
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.