To save yourself the future difficulty of cooking with an old aluminum pan that has seen better days, you're going to need to take care of the pan right from the start. One great way of doing this is to cure, or "season" as it sometimes called, an aluminum pan immediately after purchasing it. This will make it so less food sticks to it, and the less food that sticks to it, the longer it is going to keep cooking like it's new.
Wash your aluminum pan with a soft, wet cloth before you ever cook with it. Use hot, soapy water, but do not soak the pan in water. Don't wash your aluminum pan in a dishwasher, now or ever, because it will strip the pan. And don't wash it with anything but a soft cloth.
Dry the aluminum pan thoroughly with a soft towel.
Use vegetable oil to coat the pan. Use a paper towel to make sure that the entire cooking surface is covered.
Put the aluminum pan, still coated in oil, inside the oven for two hours with the temperature at 250 degrees Fahrenheit. Stay near the kitchen as long as the oven is turned on.
Let the aluminum pan return to room temperature after the two hours and then clean it with a soft, wet cloth.