Replace water with milk or buttermilk
Use melted butter instead of oil
Add an extra egg or an extra egg yolk
Add vanilla extract
Add a pinch of salt
Add sour cream or Greek yogurt
Add instant pudding mix
Add a little mayonnaise
Use coffee in chocolate cake instead of water
Add citrus zest for vanilla or lemon cakes
Mix in almond extract or other complementary extract
Do not overmix the batter
Bake only until just done
Brush layers with simple syrup
Fill and frost with homemade frosting
Add fresh fruit, jam, or compote between layers
Add toasted nuts, coconut, or chocolate chips
Finish with a homemade glaze or ganache