Garments should always be cleaned before being put away. Even if they look clean, some invisible stains, such as perspiration, take time to interact with the fabric and will appear as brown splotches later. Stop stains before they happen by having your vintage items dry cleaned before storing them.
Do not store items in plastic garment bags. They need to be able to breath, and the plastic may begin to break down and interact with the material of the garment.
Wrap in acid-free tissue paper or 100% white cotton bed sheets before folding them. This prevents damage to delicate fibers along the fold lines.
Place folded items in acid-free boxes, a cedar chest, or well-ventilated plastic boxes. Do not store in a cedar chest without wrapping in cotton or tissue—the oils that carry the cedar scent can damage fabric over time.
Only hang sturdy items like coats, and use wide padded hangers. More fragile items can be damaged by their own weight, so fold dresses, suit jackets, and other items you would usually hang if they are going to be in storage for a while.
Store all items in a cool (not cold), dark place that is not subject to extreme humidity or temperature changes. Basements, attics, and garages are not the best places for antique items.