1.
Know what model you have.
The manufacturer's name almost always appears on the dial,
but the better watch makers also keep detailed records about the
specific movements, et al. Check the back and sides of the case
for the serial number, and then contact the
watch manufacturer. They will be able to tell you all the information
you need to know about your particular watch.
2.
Get the watch appraised.
The major auction houses such as Sotheby's, Christie's, and Antiquorum
are the best, and will usually provide a watch expert. If they don't,
they should be able to recommend a respected private dealer in your
area.
3.
Get a second opinion.
Ebay is actually a good place to determine what people are currently
paying for your particular model watch. You can check the completed
auctions to see what the actual selling prices of the watches were.
4.
Sell.
If
time is of the essence, go with a private dealer: They offer the
quickest turnaround. If not, an auction house offers the possibility
of a profitable bidding war. As a last resort, you can always use
the above mentioned eBay -- just make sure to set a reserve so you
don't sell for less than you feel the watch is worth.