um... I'm no expert... but it depends on how often u play around with Flash I suppose? the more u use the program, the more familiar u get. and also, depending how u rate "expert" as, there really is no such thing as "expert".... cuz u will never finish learning all the actionscripts since new ones will come out in different versions I suppose?
anywayz... ya... lots of practice and look at lots of samples for ideas~ watch ads and movies for ideas and do all tutorials in FK... lol. those will probably help make YOU an expert hehe... good luck