Look your customers directly in their eyes when talking with them. To be sure you are looking, note their eye color.
Before a customer is finished with their transaction, ask yourself "so what is one more thing could I do to assist the customer?"
Know what your competitors are doing -- visit their website, visit their location, call them -- know your competitor!
Offer your customer the appropriate item -- a tissue, a pen, a bottle of water, a coupon, a trinket -- whatever is appropriate.
Learn one thing about your customer and remember it the next time you see them.
Incorporate social media into your advertising -- it is FREE!
What service tips do you have? E-mail firstname.lastname@example.org