Alternate tylenol and advil every ~3 hours. Give lots of long baths. Cold, soft foods if his throat hurts (pudding, ice cream, yogurt, freezies)
That's about it. It's rough - DS had it 2 weeks ago and he gave it to me. So whatever they said about adults not getting it, be careful. Wash your hands A LOT and don't share cups/food/etc. It was worse for me than DS (worse rash, and it's itchy in adults). Also: the skin by his fingers/toes and nail may peel a few weeks down the road. This is normal, don't freak out.
Give him tylenol or motrin to help with the fever and pain. There's not much you can do for the discomfort in his feet. My kid gave me HFM a few years ago and the blisters do hurt. Hope he feels better soon.