Instructions
Organize the postage stamps you intend to sell. Most individual stamps have little value, unless they are very rare or very old. However, complete collections of stamps are far more valuable. If you don't have access to a philatelist, you can generally get a decent idea of the collection's value by simply looking at common themes. Look at things like dates, subjects or countries and try to see where the most effort went into the individual collections.
Save the wrapping for the seller. Some stamps are issued with collective covers or envelopes. In some situations, the covers can be worth more than the stamps to collectors. Do not discard the covers or envelopes and do not remove the stamps from them if you are trying to maximize your value.
Go to the library to do some research. The foremost book on stamp collection is the Scott Postage Stamp Catalogue, which is available in most public libraries. If you are fortunate enough to find the complete six-volume set, it lists and attaches value to almost every stamp out there.
Talk to an appraiser. If you've looked at the Scott Postage Stamp Catalogue and think you may have a potential find on your hands, go to a registered stamp appraiser for an estimated value of your collection. Yes, its easier to simply go to a dealer, but you risk taking a lesser offer than by going to an appraiser who has no marketable interest in your collections.
Set Your price and sell. This is where you have a lot of options to choose from. You can look at doing the selling yourself online at a site like eBay. There are numerous stamp dealers in every state, including many stamp clubs and even some stamp festivals. Know your price before you walk in, however, because most of these people are large hobbyists when it comes to stamp collecting and you can easily be taken for much less than what you truly deserve. If you are looking to sell the stamps very quickly, take them to a dealer to see what they are willing to offer. You can always negotiate with them based on the selling price you came up with.