My favorite baking tip currently is to use parchment paper when baking bars and brownies.
Line the pan with parchment paper then fill the pan with baking ingredients as usual. Bake for the recommended period of time.
When the baking process is done, and the bars or brownies have cooled, remove the entire recipe from the pan by using the paper on the sides as handles. Place on a flat surface and cut into squares. This will allow you to cut the bars without working around the edges of the pan, and nothings sticks to the pan either. Makes for easy clean up.