Bring out all needed ingredients before beginning to cook. It's the fundamental idea behind what chefs call mise en place. I find this is especially useful as a home cook to determine whether I really have everything I need. If I can't find an ingredient, I can adjust the recipe or choose another dish, rather than scramble or get stuck with a half-cooked dish.
Bring refrigerated meats to room temperature well before oven roasting. I learned first hand what happens when violating this rule. My recent 9 lbs standing rib roast ended up with a wide range of internal temperatures, with the meat nearest to the bones the least cooked. Instead of one hour out of the fridge, I should have brought out the cold meat three hours before cooking.
Taste the food while cooking to adjust seasonings. I've been a bit more aggressive with salt or soy sauce with my cooking recently. Most of the time, that works well, but I've risked making some dishes too salty.
Clean while you cook. The kitchen easily descends into a pit of chaos from dirty dishes, stray ingredients, spilled liquids, and other such items, if not kept orderly. I remember a professional chef who cooked at my college fraternity who often finished cooking a full meal with the kitchen already being clean.
Keep an eye on it. This comes from a David Letterman joke a long, long time ago, when he facetiously offered this as a deeply insightful BBQ grilling tip. Any application of high heat to food needs to be closely monitored as food conditions can change rapidly from excellent to inedible.
Time the dishes to all finish simultaneously. One of my pet peeves is serving or being served hot food that has lost its proper temperature due to neglect affecting the food's timing. A related pet peeve is when the diner is the one to neglect such timing, but my point here is when fully prepared dishes sit and get cold while other dishes still need to be finished.
Account for carry-over heat. Basically, food continues to cook after it's removed from the stove or oven, leading to possible over-cooking or over-drying. For me, eggs are particularly susceptible to this.
Let meat rest after cooking. The internal moisture redistributes as the carry-over heat finishes its dispersion within the meat.
