How can I care for my postcards?

There are some definite things to avoid:

1. Don't store postcards in plastic containers for long periods of time.
2. Never keep them in the film & sticky back kind of photo album!
3. Keep them away from old craft/pulp paper style albums. These inexpensive papers contain high amounts of acid.
   

"Postcards should be kept in acid-free, archival quality storage materials, away from light. Many serious collectors keep at least their best cards in Mylar (a polyester film) or polyethylene sleeves or in special archival storage boxes or pages."

"In general, most archivists consider polyethylene, polypropylene, and Mylar stable storage media. Polyvinyl chloride (PVC) is a cheaper plastic, but contains plasticizers that can migrate, leaving an oily residue on your postcards over time. One can recognize PVC by its distinct "plastic" smell. Archival quality materials generally have very little (if any) odor."

http://www.overanalysis.org/postcards/faqsec1.htm