Instructions
Grade the condition of your doll. Antique dolls are graded for things like crazing, cracking, stains and functionality. Newer dolls like Barbie are graded according to (amongst other things) whether they have ever been removed from the box or not. Top prices are given for dolls that are in mint condition and have never been removed from their factory box. At the bottom of the grading scale are dolls that have been played with and are missing the original box, clothing and accessories (but are still in a reasonably good shape).
Do a search on eBay for completed auctions to get an idea of how your doll has sold in the past. Pay close attention to the descriptions: MIB means "Mint in Box" (the doll may have been removed) while "NRFB" means "Never Removed From Box." In general, dolls without boxes are worth at least half of what a MIB doll is priced at. Usually, prices reported in doll books or other places are averages for recent sales. You may get a lot more, or a lot less, when it actually comes to selling your doll.
Search the Internet for your doll. You may find doll shops, stores or online auctions listing the current prices for your doll.
If you cannot locate the price for your doll, obtain an appraisal from a doll appraiser. Find one online by typing "doll appraisals" into an Internet search, or visit a doll show--there are always doll appraisers at larger shows.