K Dog said...
What sort of wind range do kites have? Can you go out for a bash in 10 knots.... and be out there at 30+?
The size of the kite depends on the conditions (wind speed), the experience and weight of the kiter, and the type of board being used.
Assuming a 'standard' twin-tip that's appropriate for the riders weight...
A beginner 80kg rider can safely use a 12 m kite for ~15-20kn.
An intermediate 80kg rider can safely use a 12m kite for ~15-25kn.
An intermediate 50kg rider can safely use the same 12m kite from ~13-20kn.
An advanced 80kg rider can use (not necessarily safely) a 12m kite in 13-30kn.
Each kite has it's own wind range so even my example of a 12m kite will vary greatly depending on the specific make and model of the 12m kite.
Ideally when you start out you get lessons with a school so they can put you on the perfect sized kite and board to make the most of the exact conditions you get on the day. This means that your safe, in control and will make the most of your time on the water and the money your spending on your lessons.
Once you've had a few lessons and you have your own gear (assuming 1 kite, 1 board), then your instructor will be able to tell you what wind range and conditions you want to learn in. Attempting to learn underpowered is a very common mistake with beginners and will end in frustration, kites falling from the sky and potentially bystanders or other kiters being injured. Attempting to learn overpowered is even more dangerous as everything happens faster and far more violently.
If in doubt - don't go out!