I've been thinking about doing this. Things to go in might be:
* cleaning tips - what cleaning products are available for what jobs
* cleaning tips - how to clean skirting board/internal doors etc
* painting tips - best types of paint to use on wooden window frames etc
* history of pure water cleaning
and here's one that helps everyone ...
* list of other "partners" in your area - maid services/carpet cleaners etc. You recommend them for free - and ask them to do the same for you. Suggest to them that they produce a newsletter as well and do the same. That looks like a lot of extra publicity and goodwill for a lot of tradespeople and a lot cheaper than ads in the local paper.
Plus, of course, information about yourself and the excellent services you can provide. Are you a family business, long established, a new and exciting start-up?
If you have cleaned some famous local buildings, the snake enclosure at your local zoo or the local scout hut, that's worthy of inclusion.
A simple A4 folded into an A5 booklet could be enough to generate a lot of goodwill and maybe a few more customers.