Swann is right to remind you that you probably need an oven thermometer to check the accuracy of the oven's temp. You can't make allowances for discrepancies if you don't know they're there. Then, when baking, it's important for me, anyway, to set a timer for the correct number of minutes. I'm really good at getting busy with something else and forgetting my cake, otherwise. Even a couple of minutes too long in the oven can make all the difference between perfect and dry.
As with anything else, tho... practice makes perfect. The more cakes you bake, the more feathery light your outcome will be each and every time. and pleeeeeease,
don't use a mix! Scratch takes only a few minutes longer and tastes SO much better!