The thread on pan-cooking steaks reminds me of the issue of things that chefs do but don't always make it into recipes. Some are merely kitchen tricks (trucs) and others are standard practices that make a huge difference in how people can appreciate a recipe.
Here are three off the top of my head; I invite hounds to list more (and explain why):
1. Generally, when cooking red meat, you want the meat near room temperature before you start cooking it. Why? Because it will dramatically reduce the magnitude of after-cooking, which is when innermost flesh continues to cook after removing from heat; this then helps retain juiciness, among many other consequences. Recipes very frequently utterly neglect to mention this. It's a sign that a cookbook writer (or editor) is strong on technique when it's included.
2. Generously salt your pasta water before cooking pasta. It brings out the flavor of the pasta, which is the main flavor that the sauce should support, not obscure. Cookbooks are getting better on this score, but it hasn't sunk in in many quarters.
3. Ever wonder why restaurants serve food on warmed plates? Don't wonder. Learn. Warm your serving bowls and plates for foods served hot (and chill them for cold courses). As a recent Cooks Illustrated recipe for fettucine alfredo demonstrated to the puzzled surprise of the CI staff (why where they surprised? because they obviously failed to do this from habit....), it is often the single step between OKness and excellence. I put a big splatter screen over my pasta pot and invert my serving bowl over it; I dry the bowl out before using it, but it makes a huge difference, as does serving on warmed plates.
And for bonus points: salt your green salad before dressing it. The salt is where the salad gets its name from....
There are so many more, aren't there? Chime away.