The Image Permanence Institute of RPI wrote a report on the degeneration
of acetate-based film. The title is "IPI Storage Guide for Acetate
Film."  It has many good suggestions (Acrobat file):

http://www.rit.edu/~661www1/sub_pages/acetguid.pdf

The two main enemies of film life are heat and humidity, with heat being
of greater risk.  As an example, they estimate that film stored at 80
degrees F will only have 1/2 the life of film stored at 70 F. (25 years
vs 50 years at 50% humidity)  There is a chart in the above report that
shows the relationship.  
Film stored at 90 F, and 80% humidity might start having problems in as
little as 7 or 10 years. While daily temperature swings will of course
extend that time somewhat, you can see the detrimental effect on film of
living in a place like Singapore, where the temperature and humidity are
typically on the high side.

Overall, you want to keep the film away from anything that releases
chemical vapors, like wood, particleboard, photocopy machines, vinyl,
and so on.  You also want to keep it as cool as possible.  Archivists
seal the film in metal cans at about 40% humidity, and store them in a
freezer. That isn't practical for most people, so simply packaging the
film in sealed packages when the humidity is low, plus keeping the film
in a cool place will likely give film life of better than 50 years.