If your sub already has a foot fetish, I think you need to ascertain whether it is purely feet, or footwear and feet. Whatever it is, the first thing you must do is purchase a luxurious padded footstool about 30'' high to be on the floor in front of your favourite armchair at all times. Have your sub kneel on the floor, and get him used to this position to reinforce his status in your relationship.

Have him bring through a basin of warm water and set it aside, then tell him that you'd like your feet and toes washed but first with his tongue in between your toes, everywhere. Then have him wash your feet one by one in the basin. Then have him massage your feet for a good hour as you relax above him with some wine. Soon he'll be giving you full pedicures as you
watch tv, completely ignoring him. Then try having him polish your boots whilst you still have them on.