Many different factor can directly affect the value of both antique pocket watches and more modern collectible pocket watches.  Some of the primary things that will determine that value of your watch are listed below

What it’s made of: Watches made of gold, silver, or plate are more valuable than brass.
Is it intact?: No missing parts. In addition, having the original box, bill of sale, or other provenance papers will add to the value.

What type of condition is it in: Look for wear and tear, scratches, hairline cracks, dents, blemishes on the metal, brassing (where the gold plate is rubbed off), fading or stains on the face or repairs to the face. All functions (calendar, chimes, moon phases, etc.) should work, and the watch should have been cleaned and oiled by a professional every 2-3 years.

Quality and Craftsmanship: Number of jewels (the most highly prized watches have 21 or more); the number of positions adjusted to (usually five, often marked on the movement); and marked as adjusted for temperature.

Rarity and Historical Value: Ownership by a famous or historical person adds to the value - paperwork proving this is needed. Most engravings detract from the value of a watch, unless it is inscribed to a famous person or the inscription authenticates its presence at a historical event - a presidential event, a maiden voyage of a famous ship, plane, etc. This type of inscription is easy to fake. Look for other corroborating materials such as invoices, photos, certificates, presentation materials, etc.