Keep it out of direct sunlight. Sunlight ages 
paper. I have posters, old pulp comic books, and 
news clippings which are still in good condition 
after 10 or so years because they've been kept in 
the dark and a cool area. If you're worried about 
acid, there are kits at hobby stores, which allow 
you to deacidify them -- read about this in a 
book about comic collecting, but I haven't tried 
it myself. If you're brave, you could try and do 
what some archivists do, which is wash the paper 
in distilled water -- although the effect would 
be at best temporary, and the results uncertain 
with animation pencils. If you're really worried, 
I've heard of museums using a methyl magnesium 
carbonate solution to stabilize their documents.