Replace water with milk or buttermilk
Use melted butter instead of oil
Add an extra egg or two egg yolks
Add vanilla extract
Add a pinch of salt
Add sour cream or Greek yogurt
Use coffee instead of water in chocolate cake
Add instant pudding mix
Add an extra tablespoon of flour for structure
Mix in citrus zest for vanilla or lemon cakes
Fold in mini chocolate chips, nuts, or fruit if desired
Bake just until done to avoid dryness
Brush layers with simple syrup for moisture
Frost with homemade buttercream or cream cheese frosting
Chill the cake before frosting for cleaner layers
Let the cake cool completely before serving