From a beginner's standpoint, using 8-10 compulsories that have not been selected for the three mandatory maneuvers at that event might be a good place to start... Choose a variety that show different skills, i.e. circles, corners, shapes, landings, stalls, etc.
Each maneuver you select for your freestyle should "flow" into the next, so that when you finish one it's not far to go for the beginning of the next one... If you do end up having to cross the sky to enter the next one, fill that space with something (stair steps, loops) to do while your kite is on it's way over there.
After awhile, you should be able to modify existing compulsories into variants of your own, thus lending distinctiveness and creativity to your score... You could even adapt some before hand, if you feel up to it.
Demonstration of as many skills as possible... Within that, difficulty, variety, creativity, program, complexity.
I would recommend you check out these resources as well:
Rules Book - http://aka.kite.org/data/download/pdf/Spor...KCR_current.pdf
Judge's Book - http://aka.kite.org/data/download/pdf/Spor...KJB_current.pdf
Compulsories - http://aka.kite.org/data/download/pdf/Spor...KCB_current.pdf
(or http://aka.kite.org/iskrb_compfigs_v2.html for online viewing)
Field Directing - http://aka.kite.org/data/download/pdf/Spor...eldDirector.pdf
While you may not be judging right off, it certainly pays to absorb what it is that they are looking for... And reading their handbook will definitely help. As for the field director's handbook, they are your liason on the field... So it's important to know what they can do for you, and what their job is.
Another great resource for animated compulsories:
http://www.reeddesign.co.uk/iskcb/index.html
I'd say to review some of these items, and come back with further questions.