(as per one of my gracious hosts)
1. Don't assume everyone who walks in the door likes to read your genre. Or, for that matter, doesn't like to read it. A simple, "Hello! Thanks for coming by! Do you like to read (genre)?" is your best introduction.
2. Don't intimidate the readers by trying to get close to them. Remain seated, or if you need to stand, move back a bit and give them room to approach the table.
3. Don't brush off a potential reader if they initally show no interest. Offer them a freebie like candy, a bookmark, a pen, etc. Friendliness pays.
4. Don't get defensive if customers make rude remarks about your covers, genre, etc.
5. And most of all, if a reader buys your book, and you autograph it for him/her, don't summarily dismiss that person as "done that" and turn your attention elsewhere. Keep being friendly. You never know when they may want to get another book for a friend, relative, or for themselves.