Washing vintage items successfully starts with a thorough examination of the garment to make sure you won't ruin it with at-home laundering methods. Keep in mind some items are simply not fit to be washed at home - but many more can be cared for with gentle methods.
First, always check tags for special washing instructions and test fabrics in an inconspicuous spot for color bleeding and water reactions to ensure washability. Items with heavily dyed patterns may not be washable, as well as items made from heavily embroidered silk.
It's also important to look at the construction of your vintage item to determine whether it is suitable to submerge it in water. Vintage garments with embellishment, sequins, or fur trim should generally not be washed, as well as items with shoulder pads, heavy boning, or lining that differs in fabric type from the outer shell. These types of garments may warp or change shape when exposed to water.
Finally, if something is tagged specifically as "dry clean only" or "do not wash", it is likely not designed to get wet. In this case, it's best to leave it to the professionals. Steaming with a hand steamer is a great option for freshening non-washable vintage garments at home between wears (as well as helping banish any lingering musty smells).