Do you keep a list of your customers likes and dislikes?
It can be a good idea because then you can suggest things when their favorites come on sale. I also write down things like their birthdays and their children's names as well (because who can remember all that stuff!)
I just keep in it on my computer with all their other details (address, phone number etc) although you might prefer to keep it on an index card system if that works better for you.
The benefit of making these little notes is that the customer feels like you truly do care about them (and people BUY from people they like!).
I like to give them a little gift in their birthday month too. Usually it's something I get really cheap (doesn't have to be Avon). Customers REALLY appreciate this!