Of American-English origin, the phrase the oldest trick in the book denotes a ruse or stratagem that is still effective although it has been used for a long time.

This phrase occurs, for example, in There’s a reason Depp’s dog keeps coming up in the trial, about the court case involving the U.S. actress Amber Heard and the U.S. actor Johnny Depp, by the British barrister Charlotte Proudman, published in The Independent (London, England) of Wednesday 18^th May 2022:

“She’s mad, bad, mentally ill, a loose cannon.” Labelling a victim as mentally ill and thus not credible is one of the oldest tricks in the book and sadly it still plays out in courtrooms. It’s what I call “gaslighting on steroids”. One of my clients was told repeatedly by her ex-partner (also a mental health care worker) that she had bipolar disorder—he convinced her she was mentally ill. The family court judge said for the first time in a High Court judgment that her ex-partner had “gaslit” her. We won—but it’s a common go-to tactic by abusers.

The earliest occurrences of the oldest trick in the book that I have found are as follows, in chronological order—they suggest that this phrase may have originated in sports:

1-: From the column I May Be Wrong, by John Bentley, published in the Lincoln Evening Journal (Lincoln, Nebraska, USA) of Friday 22^nd November 1929:

Michigan always has held some mystic power over Minnesota and this was exerted in their last meeting, with the aid of two of the oldest trick plays ¹ in the book. Michigan won.

¹ In American Football, the noun trick play denotes an unusual play in which misdirection or unorthodox tactics are used to deceive the opposing team.

2-: From the column Sport Sparks, by Lou Smith, published in The Cincinnati Enquirer (Cincinnati, Ohio, USA) of Wednesday 21^st October 1931:

One of Centre’s ends pulled one of the oldest football tricks in the book against one of Xavier University’s supposed-to-be star lineman last Friday night.
“Say, buddy, you fellows really got a tough ball club. You shouldn’t have any trouble beating Wittenberg next week,” the Centre end said. “And, by the way, I have their signals. I’ll tell you all of them.”
While the unsuspecting Xavier lineman was absorbing all this bologna like a sponge, the Centre quarter back—he was in on the trick—kept shooting play after play over “Mr. X’s” tackle.

3-: From the account of a baseball match between Oakland and Portland, by Clyde Giraldo, published in the San Francisco Examiner (San Francisco, California, USA) of Monday 17^th April 1933:

Ludolph won his third game since the season started by hurling four-hit ball. Probably the oldest trick in the baseball book, the hidden ball, was pulled by Jules Wera in the sixth inning after Blackerby had tripled to center.

4-: From the account of a rugby match between the Meralomas and the Vacs, published in The Vancouver Daily Province (Vancouver, British Columbia, Canada) of Tuesday 9^th October 1934:

With the score deadlocked 6-6 in the last quarter, Pete [Wilson] sold the Vac tacklers a dummy ² after taking a kick on his own forty-yard. As they floundered into the mud he reeled off forty yards through a maze of other Vacs, then tossed the leather to teammate George Niblo, who just breezed across the last twenty yards for the deciding touchdown.
[…]
When Pete bluffed the big Red tacklers with the oldest rick in rugby’s book and broke the tie, the Vacs lost heart and soul.

² In rugby, to sell, or to give, a, or the, dummy means: to feign to pass the ball so as to deceive one’s opponent.

5-: From Science Derides the “Love-Slave” Verdict, Crying: “Woman is the Man’s Love-Master”, by the U.S. psychologist William Moulton Marston (1893-1947), published in several U.S. newspapers on Sunday 16^th December 1934—for example in The El Paso Times (El Paso, Texas, USA):

Woman’s submission to man is only a trick. It is a play upon male egotism and dominance. Man struts like a peacock and boasts about his love conquests while the woman who actually induced him to make love to her snickers with triumph in the secret recesses of her feminine soul. […]
[…]
Let him think he is master, let him strut his stuff! This pleases him, makes him think the “little woman” is a sweet, harmless creature—and so delivers him, like Samson, bound hand and foot in the bonds which woman weaves about him while his eyes are closed. This is the oldest feminine trick in the book. It never fails. It makes of man’s self-fancied superiority a love weakness that renders him vastly inferior to woman in playing the love game.

6-: From Red Peppers: Hot Sport Chatter, by ‘Tait’, published in The Cedar Rapids Gazette (Cedar Rapids, Iowa, USA) of Tuesday 7^th November 1939:

These “miracle” teams can look plenty jittery when they lose that mental mastery over a foe which stands right up and stares back when the old fish-eye stare is in order. Reports from Champaign indicate the Illini worked one of the oldest tricks in the book on Michigan when Rettinger hid along the sideline and took a “sleeper” pass ³ to score. Later the Illinois team faked an argument over a miscalled signal and the Michigan team relaxed. Bang went a snap pass from center to Smith and he scored before Harmon, Evashevski and Co. could throw up a defense. Jittery, passing wildly and fumbling, Michigan had been taken by a smart coach. The potent Wolverine offense was more ineffectual than was the case when Iowa was stunned at Ann Arbor by a series of bad breaks. They all have their days.

³ In American Football, the noun sleeper pass denotes a pass unexpectedly involving a player hitherto ignored.