Hi Margaret,
While I have come across the use of MOU's in a professional capacity within the legal industry, I have never come across one in my VA business. I am curious to know, is it a potential client that is requesting one? I can see where one might come in handy, but I would question their usefulness in regards to a VA/Client relationship.
My understanding is that MOU's are not generally enforceable, meaning they are not legally binding although this is not always the case. While I understand the theory behind a MOU, that being to qualify or describes key issues and the process going forward, I would lean away from using a document that isn't enforceable and simply move straight to a contract and avoid this extra step altogether. I would also question the motives of a client requiring such a document, but I don't know enough of the reasoning why you might need one to be able to give any more help that that.
However, I did find a template of a very simple MOU that might be what you're looking for, it is located
here. Hope that helps and good luck!