Generally, steam is your best friend when confronted with a wrinkled piece of neckwear. Light pressure from a hot (properly set) electric iron and plenty of steam can remove most normal wrinkles and creases from average daily wear. *Remember to keep your hands clear of the steam- steam and skin just don't mix!
Fingers crossed that one of your favorite designs never falls onto hard times (aka: dragged over a filthy bar floor, wadded up in a boot, used as a towline while skateboarding behind a bus, etc...). But if it does, it may be time to call in the pros... Professional Dry Cleaning is always a recommended option.