There's a thread online where people are sharing the cooking "rules" that they ALWAYS ignore . . . like "don't put pepper on steak, because it'll just burn." Here are a few that people mentioned:
1. Throwing out a whole block of cheese when there's a little mold on it.
2. Using olive oil while cooking, instead of cheaper oils with higher smoke-points.
3. Don't cook with wine, tomatoes, or anything acidic in cast iron pans.
4. Don't eat uncooked cookie dough.
5. Unsalted butter in a recipe. Some people say they use salted ALL the time.
6. Fresh herbs in a recipe. Subbing in dried herbs is easier, and cheaper.
7. Measuring dried spices. It can be a nice guide, but spice-level is subjective.
8. Using a particular color of onion. Some just use whatever they have on hand.
9. Sifting flour.
10. Don't mix seafood and cheese.
(Buzzfeed)