DO - Communicate with the bookstore by writing on postcards that show your book cover OR have numerous extra book covers printed and use the front part of the cover as an oversized postcard. Let people know you are there to have fun, even if you don't sell any books. The manager of the store often feels worse than you do, because they are afraid you won't come back. It's equally important to spend some of your time at your signing to smooze with the people who take the money from the customers who buy your books. Get to know the staff at the book store.
Book signings are an opportunity to build relationships with the book sellers.
On several occasions, after handing the booksellers my 4-color book marks and telling them a little about myself and my books, the booksellers have actually bought signed copies of my books. If I happen to sell and sign a few books to their customers while I am there. . . Several more things. Some people are too shy to ask for your autograph. Never assume the book is for them.