I've been disappointed in cake mixes lately. It seems that they come out too thin when you follow the package directions. So I tried using a smaller pan, which helped some. I think they really have less stuff in the box than they used to, but one of my local grocers had cake mixes on sale, so we bought a bunch of them.
I discovered a little trick which I know works with chocolate cake, and I'm going to try it with modifications on other flavors.
What I did was this: I added 2 tablespoons cornstarch, 2 tablespoons baking cocoa, an extra egg, and half a cup of sugar. The result was truly amazing! A tall, fluffy, moist cake. What this amounts to really, is adding a package of pudding as they require for their pound cake mixes that often show up on the box somewhere. I was not inclined to drive into town for a silly box of pudding ;>)
Good thing, really, it worked out very well! I bet that's what they really add when they say "pudding in the mix." Just some cornstarch -- they make you add the extra egg. (Cake mixes without "pudding in the mix" only call for two eggs.) H'mmm...