The value of your watch depends greatly on the model / style, age, and case composition. It goes without saying, but watches (of any mechanical quality) that have real gold cases right now are worth quite a bit more than watches with gold plated, gold filled, gold-tone, or stainless steel cases. Presentation watches like those given to employees upon retirement were often gold or gold-filled-but there's a world of difference in value between those two types of watches. In terms of age, it's much easier to date vintage Bulova watches by their 'year code' than by their serial number. If you look carefully, usually above or below the serial number, you'll see a little alphanumeric code, like L5, N3, or P6. These can be translated as follows: Lx = 195x Mx = 196x Nx = 197x Px = 198x Tx = 199x Pre-1947 Bulova watches used little symbols to show the year of manufacture.
A picture of those codes can be found here, as well as elsewhere on the Internet: Jul 24, 2011.
After 1949, the date code is typically found on the back of the case. Beginning in 1950, Bulova used a simple code to date the case. The code is a single letter and a single digit. The letter represents the decade, the number the last digit in the year. Dating cases prior to 1950 is largely guesswork. After 1949, Bulova used a 2-digit date-code which was stamped on the case back (usually near the serial number) and sometimes also on the movement (usually near the set-screw). The first digit indicates the decade and the second indicates the year.