When I started woodworking the concept of 'Sharpening the Sharpening Stones' was completely foreign. However, the more you think about it, the more important it is.
The general principle to sharpen, joint or plane any object is make your working edge as flat as your reference. In practice your reference must be flatter and harder that the object your working.
To sharpen a chisel (as I've written before) you flatten the back and the bevel to be uniform and flat meeting at an angle. This is done by repetitive movements of the metal on a stone which wears aware the high points of the metal making it flat. Overtime however the stone is also worn aware. Eventually a slight hollow is formed. This is most noticeable over the the most frequently used areas. At this point your stone is no longer flat and cannot act as a reference. Blades sharpened on this stone will no longer be flat but contour to that hollow.
The hollow needs to be removed by flattening the stone against a hard reference surface. Nearly any of the described sharpening options will do... including wet & dry sand paper, a larger wetstone, dimond paste on a metal reference. However, after searching the net the easiest and best is the DMT Dia-Flat.
The DMT Dia-Flat is a serious piece of stainless steel (about 8mm thick) impregnated with 95 micron diamond particles. (The packet said something like 1.5 carats worth).
With a bit of water as lubricant you simply rub your water stone on the Dia-Flat until it's flat. Some people recommend marking the surface of the stone with pencil to know which section is being worked, in my case the stones were dirty enough. My stones needed a bit of work but the progress was quick and easy. Not a cheap product. But a recommended one.