I agree with Ebay as the best way to sell your gown however you want to market your dress so it stands out from the other 4000 dresses listed!
In your title list the size of the dress and if it is a designer gown, the the maker. Putting in "Size 10 wedding dress" is not going to get as many hits..Be more specific in the title:
Maggie Sotterro Wedding Gown Size 10 strapless a-line
People will search for the designer labels, the style and the size..so make sure those go in your title if possible. If you never wore the dress..then put NWT (new with tags) in the title. or NWOT (new without tags). and make sure your put that it was never worn.
If it was worn put in your description that it has been dry cleaned, has no spots. I would say to look for a photo of the dress from the dress maker and use that as the photo..why..because no bride wants to see another bride in the dress...regardless if she's buying it used..Example - if you bought the dress from Davids Bridal..find the photo of the model in the dress from their website, right click on the photo and save it to your computer and then upload that photo to ebay. The more professional looking the photo, the better it will sell.
If thats not possible - then see if you can get the dress onto a dressmakers dummy and take a few angle shots...take one front photo, one photo of the back with the train down and spread out and one closeup shot of the bodice of the gown where usually the detailing is. Whatever you do - dont submit a photo of the dress hanging on the hanger or lying on the bed people will blow by it cause they can't see the detail...in which case then submit a photo of you in it and just block our your face.
Also definitely put in a reserve amount - costs like .50 cents more but worth it - be realistic..if you bought it for $900 - you'll be lucky to sell it for $300..so set the reserve at $225 or something.
If no success on Ebay - then definitely try a consignment shop. I'm positive they'll sell it but it will cost more money out of your pocket.
Good luck!