Baking level cakes is something almost every home baker wants to do, but it seems impossible. It becomes an issue the first time someone unrelated to you is going to eat your cake, or when you are baking a cake for an important event like a baby shower or wedding. Even the most uneven cake tastes delicious, but you want your party cake to look nice, too.
The first step to baking level cakes is to ensure that you follow the instructions. Beating the eggs or batter too much or too little can lead to cake disaster. Next, make sure that your oven is at the right temperature. I don't mean check the dial to see that you've set it correctly, I mean you have to use a second thermometer to ensure that your oven is hitting the right temperature. Many ovens heat incorrectly, either too hot or too cold. Be sure to preheat your oven so that the cake goes in at the right temperature, too.
Some cakes need to 'climb' the sides of the pan, others need to have lubrication on the sides to prevent this. Again, follow the instructions in your cake recipe. There's a reason it says to grease and flour the sides - or not!
Using the right size pan, or the right amount of batter in the pan is crucial, too. The middle will always bake slower, giving the gas bubbles more time to expand before the cake 'sets' around the bubbles. If your pan has too much batter, the difference between the middle and the sides will be more pronounced.
Lastly, and especially important when baking special cakes, and especially larger cakes, there is some equipment that will help you. Even regular sized cake layers benefit from cake baking strips, which insulate the sides of the pan to give the whole cake a chance to heat evenly, which in turn leads to a better chance of baking level cake layers. There are several kinds of strips available, from silicone to cloth. For larger cakes, you'll want a 'core', which is basically a piece of metal inserted into the middle of the cake batter to speed up the heating of the cake in the middle. In combination with the cake strips, the heating core will lead to the most level cake layers you can get.
As you can see, there is no mystery to making an even cake - the right temperature, the right recipe, and the right equipment will have you baking level cakes like a professional.