I thought I would share some of my tips that I use when I'm doing a cake.
I like to use the cake mix extender recipe
Cake Mix extender CakeCentral.com. Not only does it give the cakes a nice moist flavor, but it also fills out the pans nicely.
I bake the cakes at 25 degrees less then what the box says. The lower temperature helps to reduce the hump in the middle of the cake and helps keep the cake moist. So if using a conventional oven, it would be baked at 325 degrees. Or if you're using a convection oven (which I usually do to help prevent hot spots), then you bake it at 300 degrees. However, make sure to check the actual temperature of your oven as some ovens may be off a bit and will require recalibration.
I preheat the oven 50 degrees higher then what I plan on baking the cake at. I do this because when the oven opens up to load the cake, it'll lose some of the heat. As soon as I put the cake into the oven, I'll reduce the temperature by 50 degrees in order to bring it to the correct temperature.
I grease my pans with homemade pan grease. I make the pan grease by mixing together equal amounts of flour, shortening, and vegetable oil in a mixer until it resembles a liquidy paste. I liberally brush it into the pans. Sometimes I'll line the pans with a piece of parchment paper as added protection.
I also like to use the bake even strips for the pans. This helps to keep the sides of the pan cool so that the cake will bake more evenly and reduces the risk of a big hump in the cake. Also for bigger cakes, I'll use an upside flower nail that has been brushed with the pan grease and insert it into the middle of the cake.
As far as mixing the cake, I'll sift together the cake mix, flour, sugar, and salt into a large bowl. This takes out any lumps and make the batter much smoother.
I make sure my cold ingredients come to room temperature before using. I place the liquid ingredients into a mixing bowl and with the wire whisk attachment, I mix them up for about 30 seconds on the low speed.
Then I add in the dry ingredients and turn the mixer to speed 2 for 30 seconds. I stop the mixer and scrap the bowl. Then I turn the mixer to speed 4 and mix for 2 minutes. I then immediately pour batter into the prepared pan(s). After doing so, I'll lightly drop the pan onto a counter a few times. This will help release and pop any air bubbles that are in the pan. Then I place the pan(s) in the center of the oven, making sure that the pans aren't touching each other or the sides of the oven.
Cooking time will vary depending on pan sizes used. Make sure you don't open up the oven very often, especially in the first few minutes of cooking; this could impede the baking of the cake. I check for doneness by inserting a toothpick into the cake. I try to look for a little bit of crumb on the toothpick, but not wet. If I need to, I'll bake the cake a few minutes longer.
After cakes get pulled out of the oven, I'll lightly shake the cake in the pan from side to side to help loosen the cake from the sides of the pan. I let the cake cool for about 5-10 minutes. Then I turn the cake out onto a cooling rack and then I flip it again on a plastic wrap lined cooling rack, that way the cake will be right-side up again. I'll bring the sides of the plastic wrap up and completely cover the cake, making sure to smooth out any air from the plastic wrap. Then I'll let the cake rest for a few hours until it's cool enough to work with. By wrapping it in plastic, the steam from the cake will stay inside of the cake and help keep it moist. Some people like to put their cakes in the freezer right away after they wrap the cakes because they feel that it also aids in moistness. I haven't done this as I find that just leaving the cake out on the counter wrapped in plastic works just as well in keeping it moist.
I hope these tips help anyone else out.