Always have something that you can give away to someone whenever they ask for your book. Business cards, flyers, order forms, book marks, coupons, whatever - if possible, give the potential customer something tangible to remember you by.
It should always feature the book in some way - or a creative tie-in - it should also always include a way to contact you or the publisher about buying the book.
Since sometimes it takes seeing something three or four times before they buy it, then no matter what - even if they throw the marketing material away - they will have seen it again. "That's twice!"
Business cards are easy and inexpensive to make. Flyers with order forms are also quite easy to make or have made. Use your business sense to get the best bang for your buck.Higher end promotional items shouldn't be purchased in the beginning, as much of the book project should support that. Let the profits that come in from the book finance promotional purchases like that.
Hint: Put two bookmarks in every book you sell, one that will stay with the customer who bought the book and one for them to give to their friend, assuming they will recommend the book. This makes them look good and the friend will hold on to the bookmark, so there will be no problem for them when remembering 'What was that book's name again?'
