My old prepress trick of soft-proofing in Photoshop vs now holding a printed proof under my desk lamp
For 3 years I trusted the soft proof on my screen and shipped dull greens to a shop in Fresno, until a press guy there handed me a folded proof and said "hold it next to the lamp, not the monitor," and now I always print one test sheet before a full run, so what's your go-to check before you commit a color to paper?