Foot sessions mean different things for different guys.
For me it starts off with caressing and massaging her feet and toes. Then it's all about exploring, kissing, licking and sucking every inch of her feet with my mouth and tongue. It's only about her pleasure and that in turn will turn me on.
Something like this:
m.xhamster.com/videos/nice-feet-worshipped-2064648
Oh and I agree - her feet must be clean to begin with, unless we agree that i will wash her feet beforehand as part of our session.