When I take on a customer I always ask for their name and phone number. When I print out a work sheet; I've the customers details against the houses I'm due to clean. It assists me remembering their names.
Also, I often meet customers in Tescos, or round and about, and always call them by their name when I say 'hello'. I like to be formal with them, particularly my older ones, so I call them 'Mr' or 'Mrs' whatever. This also saves you remembering two names. If the husband of 'Mrs Smith' answers the door, you know it's 'Mr Smith'.
Many of my customers make an effort to remember my name too.
They call me 'Ken', which is strange, since all my friends call me 'Tosh', but I think 'Tosh' sounds a bit 'Yobbish', so I'm 'Ken' to my customers.
I put Wor Lasses and my name on all our stationery.
It's only a small thing, but I think it's a nice touch to call your customers by their name.