The most important thing is practice. Start with small steps - don't try to do
everything at once. Start with some simple figures, then design and try out
some short sequences. Once you're comfortable with flying them, try to fly them
inside the aerobatic box. Then you can start to increase the complexity of your
figures and introduce some longer sequences.
Always check your flight from the tower view in replay. This is the way that
the judges will look at your flight.