1. Ask people. End each sale by saying: "Thank you. I hope that you will tell a friend about this." If you have a happy customers, you have people who might love to support you. You just need to remind them; and let them know that you appreciate it.
2. Give customers something that will start them talking. The best ideas are things that they will give to the next person they see. It can be a flier that you print out; or you can print you name and logo on an advertising specialty item that your customers will pass along.
3. Make it easy for your customers to talk to more than one person about you. Instead of giving them one sample or coupon, give them several. If you give someone five samples, some people will look for five other people to give them to.
There are a lot of other things you can do to get more word of mouth advertising. If you only do these three things though (and do them regularly), you will get the most results fastest. Make sure you are getting the easiest stuff done before you try doing too much of the more time consuming tasks.