Favorite: Use a lid while cooking... pretty much anything in pretty much anything. Doesn't have to be the "correct" lid for the pot/pan/skillet/etc just something to cover the food while its cooking.
It traps heat so you can lower the cooking temperature, heats the top more evenly with the bottom (I make pretty substantial omelettes every morning and it definitely makes a difference), keeps moisture higher under the lid that can reduce scorching and sticking.
Runner Up: A lot of recipes seem to be modifications of a basic "thing". Examples from when I started looking closely at recipes... Pancakes, waffles, and cakes are just tweaks on a similar recipe that are cooked in different ways with some different ingredients. "Cream of Something" soups and gravies are just slightly different versions of each other.