On 27th April I attended a workshop at the Arthouse on 'Approaching Galleries'. Karen from The Cupola Gallery in Sheffield led this, and she gave us lots of practical advice. She runs a commercial gallery, so her suggestions were mostly concerning how to contact this type of gallery. But her comments were just as useful for working with other galleries.
Her main message was to be as professional as possible in your relationships with galleries.
Visit any galleries that you think you'd like to exhibit. Get a feel for the place.
Use the recommendations of other artists.
As a means of making the initial contact with a gallery, write a letter to them. Find out the name of the contact person, and address your letter to that named person.
Ask for any 'submission guidelines'.
Write a formal letter, using correct grammar and punctuation. Use headed paper which includes an image of your work.
Write a little bit about your work - talk about the process and the context concerning it. Write as though you know what you're talking about. Sound confident, and as though you are an expert about your work.
Include your contact details, and your e.mail address, as well as your business card. Include an image of your work on your business card.
Also include an 'approximate price range' of your work, for example, '£100 - £2000', or 'prices start at £100' etc.