It follows that it is important to have the nut and bridge slots correctly cut. This is a vital detail that is often overlooked. The bottom of the slot should be U shaped, not V shaped or rectangular in cross section. The slot should be neither too deep, too shallow, too narrow, too wide nor too long. Here we are moving into the realm of setup.
Many players use graphite to lubricate the nut and bridge slots.
A common technique is to use soft pencil lead. You have to keep the pencil point sharp to reach the bottom of the narrowest slots. Use the softest pencil you can buy and try to get as much lead into the slot as you can. I think the jury is still out on this one. Delrin is a very low friction material, but seems to be too soft for mandolin nuts, as the strings dig into it.