I use different techniques depending on the flavor of the mix. My two most common flavors are chocolate and vanilla, so I will share what I do for each of those. If you have a flavor that you want me to discuss, just ask in the comments.
Vanilla Cake Mix
1. Use a good vanilla cake mix like Pillsbury Moist Supreme, Duncan Hines French Vanilla or Betty Crocker Golden Vanilla. I like these because they are readily available in my supermarket. When I plan ahead, I will buy the King Arthur Vanilla cake mix from their website.
2. Add in an extra egg or two.
3. Replace water with whole milk.
4. Add in 1 teaspoon real vanilla or 1/4 teaspoon almond extract.
5. Use melted, unsalted butter for the oil, doubling the amount of oil called for on the box.
6. Add 1 teaspoon lemon zest.
7. Add in 1 snack pudding cup of vanilla pudding.
8. Add in 2 tablespoons of mayo.
Chocolate Cake Mix
1. Add in an extra egg or two egg yolks.
2. Use hot water instead of room temperature or cold water.
3. Add in 1 tablespoon of coffee.
4. Use melted butter in replace of oil, using twice the amount called for on the box.
5. Add 1 snack pack pudding cup in chocolate.
6. Add 2 tablespoons of mayo.
Other tips: you can replace all the oil with applesauce in equal amounts. The cake will tend to me a bit drier but does cut down on the fat content. Replace milk with buttermilk and add 1/4 c more than the directions ask for.
Be sure to check the temperature of your oven. If you overbake or underbake, your cake will not be at its best. There are oven thermometers you can purchase to help you with this.
I also like to use the best pans I can afford. I have had my cake pans for years and I love them. The heavier pans heat more evenly but are more expensive. Try your local kitchen store or look for some online.
I hope these tips have helped you out and that you get a delicious cake to share with family and friends. Do you have any tips for me to try?