Always use fresh, eggs at room temperature - this ensures they will whip up really fluffy. Separate out your egg yolks from whites and whip your egg yolks with your sugar until a pale yellow colour. Use a mixer to bring your egg whites to a meringue consistency, these should then be folded into your other ingredients last. Using baking powder always helps too.
Lastly, never check your cakes for readiness until they have had at least 2/3rds of their allotted time in the oven.