Many of us have letters, books, photographs, maps, certificates and various papers of sentimental, intellectual, or family interest, which often are not looked after properly.
We recommend storing precious documents and photographs in acid-free envelopes and boxes. Keep them in a dry place, preferably with a steady temperature. Most damage that they suffer is caused by a combination of factors, primarily too hot or cold a temperature, poor storage conditions, sunlight, and improper or no protective packaging. One or more of these situations can lead to mould damage, discolouration of paper and inks, and might encourage pests such as mice.
The National Archives has produced a series of videos about safe handling techniques for different document types which you may find helpful.