I am also a BA cadet who was accepted in 1999.
My advice is similar to WiseAlderman (fine pub by the way). There are pieces of good advice on here, but a hell of a lot of c##p. BE very, very selective when taking advise from this forum.
Just be yourself. BA and any other employer will eventually find you out if you are trying to be something you are not. When I applied, there was heavy emphasis on understanding the business side of the airline. Most reasonably intelligent people can be trained to fly aircraft, so BA wanted people who understood the industry and the dynamics of the business. When the cadet scheme re-starts (which it will), I'm not sure if this will still be the case, or if the criteria will have changed.
That said, good luck! Whatever people say, there are places up for grabs, and you should believe in yourself. You never know, you might be pleasantly surprised!
Cheers...
Mary