The Springy Centre
The middle of the cake should feel a bit springy to the touch. As the cake cools it will continue to bake slightly from the residual heat, so taking it out at this point will ensure it doesn't over bake even when it's out of the oven.
Check the Sides
Generally the sides of the cake will start to pull away from the sides of the cake tin. Although the edges of the cake might look a bit dry, they should still be a deep golden colour and not crisp and dark.
Use a Cake Tester
We use cake testers all of the time at Baking Mad but you could use a tooth pick or a kebab skewer if you don't have a purpose made one. Simply pop the tester in to the middle of cake. It should come out clean if the cake is baked. If however, it comes out covered in batter (no matter how little), pop the cake back in the oven for a couple of minutes and keep checking with the tester until it's done.
Take the Temperature
If you're really nervous about your cake baking properly, you could use a thermometer to test the internal temperature of the cake. Generally you should measure the temperature of the centre of the cake and it should read around 99ºC