Since egg whites can dry out a cake, try using just egg yolks or add an extra egg to the mix. Over-stirring batter is also a no-no, as it leads to a dry, chewy cake. As simple as it sounds, the most important tip for baking a moist cake from a box mix is not to overbake the cake. Check for doneness 5 to 10 minutes prior to the recommended baking time. If a toothpick comes out clean, remove the cake from the oven. Use a thermometer to test the actual temperature in your oven. If your oven is running too hot, your cakes will turn out too dry.

Almost all boxed bake mixes call for added liquids and fats. Fats in particular are important for creating a moist cake, as they reduce the amount of cake-drying gluten. Use whole milk instead of skim or reduced-fat milk. If the mix calls for oil, try using extra-virgin olive oil. You won't be able to taste it in the final product, but olive oil contains natural emulsifiers that improve cake moisture and texture. However, if you're on a reduced-fat diet, use applesauce instead of the oil.

Adding a box of instant pudding to a cake mix will help produce a moist cake and boost flavor. Experiment with different types to use in cake mixes, such as chocolate pudding with chocolate cake mix or banana pudding with yellow cake mix. Prepare the mix following the instructions and simply add the dry instant pudding and mix until blended in. For a little extra moisture, add an additional whole egg along with the dry pudding mix.

Mayonnaise isn't an ingredient that seems like it belongs in cake, but mayonnaise is simply a blend of oil and eggs with a touch of acidity. It adds moisture to a cake and no one will be any wiser when tasting the end result. Add at least a tablespoon along with the other wet ingredients or up to one-fourth cup, and you'll end up with a moist, creamy confection.

Yogurt and sour cream may seem too sour or bitter to add to a cake mix, but the acidity will help to tenderize gluten and prevent the formation of drying proteins. Add 1 cup of sour cream or yogurt instead of the other liquids or just replace some of the liquids with buttermilk, yogurt or sour cream. Another secret that pro bakers use is to dissolve sugar in an equal amount of water in a saucepan and lightly spray the solution onto the cake before adding frosting.