Malgus summed it up pretty well. Keep your feet dry. Wet skin is soft skin and soft skin blisters easily. One thing I would add is duct tape. In a pinch you ccan put some padding overthe blister and then cover in duct tape. The duct tape will act like a tough layer of skin and will reduce friction since the outside is slippery. Maybe it is just psychological but if I am in the direct sun for long periods of time my feet feel hotter with dark colored socks. White cotton socks are all I wear.