If you own artwork and would like to sell it at a gallery, call the appropriate gallery to see if they are interested in what you are offering. If they express interest, submit photographs of the artwork and information including artist, title, size, medium, date, provenance and price.
If you do not know the fair market price for the work, the gallerist can help you. The seller needs to make sure that the work is "retail ready" before it enters the gallery. The gallery will usually cover costs for promotion, documentation, insurance, shipping and presentation.
The options for selling are an immediate sale or consignment sale. In an immediate sale the work is paid for upfront by the gallery. With work on consignment, a consignment form is issued stating the commission terms and agreement. A seller's commission typically ranges from 20-30% of the sale price and is paid to the seller shortly after the sale of the work. Consignment contracts generally run from 6 months to a year and are renewable by mutual consent.