Hello! Taking care of your feet is VERY important on the Camino. This can't be emphasised enough. My first Camino was the Frances from St Jean Pied de Port in 2008. I wore lightweight hiking boots. I also had cotton (summer weight) Bridgedale walking socks and liner socks. I've worn this boots in the Scottish highlands, in the Alps, in the Pyrenees and in South America and I never had a problem until the Camino. I developed very painful blisters under by big toe and on the side of the big toe and was taking a lot of Ibuprofen. I took a rest day in Logrono and my walking partner located a sports shop near the hotel. I decided that I didn't need walking boots as the route wasn't rough enough to need ankle support. So I went for a summer weight walking shoe (Merrel) with a vibram sole (good grip on wet rocks). I tried on my normal size and it hurt. I kept on going up sizes until I was three sizes larger than what I would normally wear. The person in the shop explained that on the Camino, due to the heat and lack of adequate hydration, people's feet can swell quite a bit. I posted my boots home and continued the Camino in my new walking shoes. By blisters were still covered by compede, but they actually healed along the route. By the time I arrived in Santiago, my feet were perfect. We picked up some unguento de peregrino in Tricastela. This is a vaseline based product that has arnica and other herbs which are good for feet. If you can't find this, vaseline or even Vick Vapo Rub works well. You put a very light coating on your feet in the morning and then put on your socks. If you are walking for long distances, take a break, take off your socks and let your feet and socks dry. Recoat your feet, put on your socks and set off again. You need to get proper walking socks. If you have blisters, the light coating of vaseline or Vicks helps prevent the compede from becoming one with your socks. I would also VERY strongly recommend a pair of walking sandals, like Teva. At the end of the day, it is wonderful to take off your walking shoes and put on your sandals. I am a convert to walking poles. As someone suggests, you should get some rubber tips for them and duct tape them on. Go for collapsible poles that can be strapped onto the side of your rucksack. I find poles useful for uphill walking and VERY good for coming down hill (you can adjust them to make them longer). Your knees will thank you.
Again, listen to your feet. If you think you have a hot spot or blister developing, stop and check it out. Don't be pressured (as I was) into pushing on to the next down. I use compede for blisters. Spanish people like using a needle and thread. You thread the needle, pierce the blister and let the ends of the thread dangle from each end. You can move the thread back and forth to reopen the puncture and let the fluid build up out. A chiropodist I know was horrified by this as he said that it was a sure way to bring infection into the wound.
A final recommendation would be pre-trip foot preparation. If you take a few grains of potassium permanganate and soak your feet in it for 10 minutes per day, you end up with rust red feet, but your feet don't sweat! This recommendation came from my chiropodist friend. You can also use rubbing alcohol on your feet to toughen them up pre trip.
Buen Camino