Don't use paper clips or rubber bands on your precious papers. Store them in a climate-controlled place, preferably at a low temperature. Don't store them near outside walls, or near fireplaces where temperatures may be erratic. Regulating the humidity can help prevent mold, or conversely, the paper drying out and becoming brittle. Store the documents where light can't reach them.
Light can cause paper to yellow and ink to fade.
Ultraviolet rays from sunlight or fluorescent lights can also cause invisible chemical reactions that may further damage the documents. For extremely valuable documents, you may want to store them in a safe-deposit box. This can save them from fires, floods, or other disasters that may occur. You may also want to transcribe the document, but if you use a computer, keep in mind that hard drives may crash, disks can be erased or damaged, and the formats of today may be unreadable in a few years. Always keep hard copies of transcribed documents in several safe places in case of one of these technological problems arise.