I think the most important is to first of all have a comfortable, fitting and supportive pair of boots/shoes. These should be broken in well before the hike. Wear them every day before setting off. I wore my boots for walking around every day for about 2 weeks prior to my walk, but still had some problems for the first week, after which they were quite broken in. Make sure you have a good pair of hiking socks -- bring 3 pairs, and wash and change them every day. Also, do not bring too much -- a maximum of 10% of your body weight seems to be a good estimate. I actually used a small kitchen scale to measure every piece of equipment I had -- bringing only the ones with lightest weight and maximum utility. You need less than you think you need. During the walk, I carried a 5 to 6 kilo backpack, with about an extra kilo weight once some water and food is inside.
My sister and I were also very careful to prevent foot and leg problems by following some routines every day, as follows:
- At the end of a day of walking, and before sleeping, take a lot of time to massage your feet, ankles, calves, knees -- even if it does not yet hurt or if it does, wherever it hurts -- preferably with some ointment to get the swelling down. I used Voltaren gel -- an anti-inflammatory gel -- but not too much as it also has some medicine;
- Elevate your legs (90 degrees if possible) to rest them before sleeping;
- At the start of every walking day, and before putting on your socks and shoes, put some ointment on your feet to prevent blisters. I used Hirschtalg and Milchfett -- available in Germany -- they are some kind of medical salve/ointment -- I am not sure what the equivalent is in English, though. If some area still feels swollen, I put a bit of Voltaren gel. My sister used a blister stick salve from Compeed. You can get these along the way in some of the pharmacies;
- If you feel some part of your feet chafing or possibly getting the beginnings of a blister, immediately put some Compeed blister tape( I think these are really the most effective-- we tried other blister tapes but they were not as good). If you already have a blister, then drain them at the end of your walking day with a sterilized needle (wipe needle with alcohol or iodine/betadine) or pass a needle with thread through your blister, until all the water drains out, then put betadine. Leave the blister uncovered to dry overnight. Next day, cover up with blister tape again before starting your walk;
- Bring some support sandals to change into at the end of walking day so as to rest your legs and so as not to constrict your tired feet (I had Tevas);
- During your rest stops, any time that your leg/feet areas feel tight or hurt during your walk, stop and do some light stretching. You should also do these at the end of your walking day. The ones I did were: standing quadricep stretch, hamstring stretch, calf stretch, glute and piriformis stretch, chest stretch (see video: http://www.runnersworld.com/stretching/the-body-shop-happy-endings), as well as plantar fasciia stretch (http://sportsmedicine.about.com/b/2007/01/05/new-stretch-decreases-plantar-fasciitis-pain.htm), and standing illiotibial band stretch (http://sportsmedicine.about.com/od/flexibilityandstretching/qt/ITBand-Stretch.htm).
- Make sure to always hydrate, meaning to drink a lot of liquids -- water or electrolyte drinks. We drank a lot of an electrolyte drink called Aquarius, during rest stops along the way.