I have two:
1. When baking breads (banana, cranberry, etc) or cupcakes/muffins, preheat the oven 25 or 50 degrees lower than the temperature you are going to be cooking at. Then when you are about to put your goodies in the oven, turn the heat up to the correct temperature. Whenever I do this, the tops of my breads/cupcakes come out perfectly rounded. If I don't do it, they come out ugly and weird (though still delicous).
2. While this may seem obvious to some, if you are using silocone bakewear, put it on a cookie sheet before you put it in the oven so they have a sturdy surface to sit on. My mom had been using this silicone muffin top pan and whenever she would take it out, at least one would plop out onto the bottom of the stove.