First up is overcrowding the pan. Too much food in one spot traps heat under the food, creating steam. That can translate to a product that's limp. You want a browning effect, which seals the exterior and locks in moisture, so cook in batches for your best bet.
You also want to refrain from adding food until the pan's surface gets hot enough. A hot, oily surface creates a nonstick environment - the one your food will love for sautéing. Put the pan on heat, add oil or butter, and then test a drop of water. If it dances, the food is ready for cooking.
Slow and low is the rule for cooking meat, but too low for too long can dry food out. So for protein, crank the heat up to medium-high for the first couple of minutes to really heat up the pan. When you add the meat, it will sear the exterior, sealing in moisture. Then lower the heat.
Another mistake is turning too often, too soon. Give food a chance to brown, especially proteins. To test it, lightly nudge or lift a corner to see if it's ready to release from the pan for flipping.
Adding garlic early when sautéing other veggies, like onions and mushrooms, will cause scorching. So save the garlic until later, because it cooks faster than other veggies.
When baking, cold dairy and eggs don't mix well with dry ingredients, so let these foods sit out for about 30 minutes to an hour for better results.
Another baking mistake is using liquid measuring cups to measure dry ingredients. As it turns out, you get too much as flour compacts, leaving your baked goods dry. Fill a dry measure cup by scooping and sweeping the excess off with a knife for best results.
And if you haven't heard it before, don't put your tomatoes in the refrigerator, because it makes them mealy. Instead, leave them on the counter until you're ready to use them.