This usually happens one month after publication, and it's OK to wait for them to contact you. Sell your book. This is when you find out why the big publishers only bet on certainties. You will have to use every marketing trick you can dream up to get your title noticed. Bookshop managers are used to dealing with reps from the big publishers who have advertising money to burn, so they will not be impressed by someone with a couple of paperbacks in a briefcase.
Mail order is good.
The customer sends cash with their order, you bank the cheque before mailing the book. In Print database. This may generate some sales, as bookshops search the subject index for their customers. Negotiate hard over the discount they want. Remember that they will take a minimum of three months to pay-up after each sale.