The classic way to wear a pocket watch is with a waistcoat (vest). The watch sits in one of the lower waistcoat pockets. Its chain runs across the front to a buttonhole or to the opposite pocket. The chain is not just decoration: it keeps the watch secured if it slips from your hand while you check the time.
Choosing the chain. A single Albert chain has a bar (T-bar) at one end that passes through a waistcoat buttonhole, and a swivel clip at the other for the watch's bow. A double Albert has two arms: one holds the watch and the other holds a fob, seal or key, and the bar sits in the middle buttonhole. A short fob chain or leather strap hangs from a trouser waistband or belt loop. It is the usual choice when no waistcoat is worn.
With a waistcoat: put the watch in a lower pocket and pass the T-bar through the buttonhole in line with it. Leave enough slack so you can lift the watch out and read it at a comfortable distance, but not so much that the chain sags below the waistcoat hem.
Without a waistcoat: the watch pocket on jeans or trousers (the small 'coin pocket') was originally made for a pocket watch. Clip a short chain or strap to a belt loop and let it run into that pocket. A belt clip works the same way. Avoid loose trouser pockets that also hold keys or coins, because these scratch the crystal and case.
Open-face or hunter? An open-face watch shows the dial straight away. A hunter case has a hinged front cover that protects the crystal and is opened by pressing the crown or pendant. Hunters were favoured for rough use. Open-face watches became standard for railway service because they can be read quickly.
Looking after a worn watch: wind it at the same time each day. Keep it away from strong magnets such as phone cases, laptop lids and speakers. Do not wear an old watch in rain or while doing physical work, because most antique cases are not water-resistant. If a hinge feels stiff or the bow is loose, have a watchmaker check it before it fails.
Etiquette is flexible today. Historically, the watch chain was part of formal and business dress. Today it is a personal choice, and the only firm rule is practical: the watch should be secured, easy to reach, and protected from knocks.