Gareth

It starts with learning the basic pattern, then from there go on to understand the bunkai (the meaning of the kata), each move is an attack or defence against an opponent. The final key ingredient is visualisation of your opponent, this allows you to work on your kime (timing, power, speed). For shotokan kata Kanazawa Sensei is a great example for you to follow, you can find a collection of him performing all shotokan katas at http://www.karateinternetvideos.com/shotokan-kata