It's easy. I use 6"x 4" stock cards to record customers payment.
If you use a book to list your customers, do this, write their name, the job price on the left hand side, then draw a series of downword lines in your book so that the page is made up of small squares. each column of squares is a months work. I put in 12 columns, A years cleans. If they pay when you finnish the clean tick the next available square next to their name. If they are out write a 0. This gives you a record of payments received. If you call back later and they pay, strike a tick through the 0. If I get any knock backs they get a dash in their square for that month. Three dashes on one card and their looking for a new WC.
If you put a dash in every other square you know to leave them that month. You can make a table in microsoft word to suit your purpose.
I put stock cards in the printer to draw the down lines where I want them.
Each street or working area has it's own card. These are kept in a plastic envelope which in turn is kept in a 6x4 photo album.
I hope I'v explained it right, it's a good system. dai