A great deal depends upon the soap. A lot of guys here may disagree with me, but I found that the gel generally does a great job of lubricating my scalp. HeadSlick also is a great product.
As for soaps, there are some great and inexpensive shaving mug soaps out there like Van der Hagen and Williams that make a great lather. (I tried a glycerin mug soap a little while ago. Not a good choice.) Right now, I am using a plain olive oil bar soap I got at a health food store and cut to fit my mug. Best stuff ever for me.
A preshave oil like Shave Secret or Somersets cuts down on the friction too.