Digital Artist Glove.
This product was originally created for the digital art industry, where artists are working on touch-screen digital tablets. They had a need for something that would prevent their drawing hand from creating random marks on their drawings as a result of friction if they rubbed it on the tablet surface.

These lycra gloves were the product that filled that requirement. They slip easily across the drawing surface creating very little friction.
So when I found out about them I thought that there was a possibility that they could also work for pencil artists too.
I used to lay a piece of clean paper onto the my drawing, so that I could rest my hand upon it to keep my drawings clean, but by using one of these gloves, I can achieve the same benefit, but with much less hassle.
They are made so that you keep your thumb and first two fingers free to hold your pencil, but the two fingers that are most likely to come into contact with your drawing surface are shielded by this slippery material which is much less likely to smudge your drawing if they touch it.

NB: I should say at this point that if you are using very soft pencils, then there is always going to be the potential for smudging to occur, whatever strategy you adopt.

They can be purchased for anything from £2 – £8 (They all seem fairly similar, so for once I don’t think there is much benefit to be gained in buying the more expensive ones).
I have two gloves, so I can wash one regularly and always have a clean one to use.