Replace water with milk or buttermilk
Add an extra egg or use only egg yolks
Use melted butter instead of oil
Add sour cream or Greek yogurt
Add instant pudding mix
Add vanilla extract or other extracts
Add a pinch of salt
Use coffee instead of water for chocolate cake
Add zest, spices, or cocoa powder
Fold in chocolate chips, nuts, or fruit
Brush layers with simple syrup
Frost with homemade frosting
Bake in smaller pans for thicker layers
Do not overmix the batter
Check for doneness early
Let the cake cool completely before frosting