I've done a few long walks in my time and the main thing I would say (once you've got your kit as comfortable and lightweight as possible), is that you need to give a lot of thought to your feet. A good blister kit has already been mentioned but you should go and get a few blisters in the build up to the trip and develop a good method of dealing with them that works for you. I get a padded plaster like 'compeed' on my hotspots as soon as they appear as a preventative measure. If a blister does develop and I still need to continue walking then I pierce it with a sterile needle, drain it and get the compeed plaster on, sometimes backed up with some wide zinc oxide tape to hold the plaster in place if it's an area that's getting a lot of rubbing.
If you are used to walking and running then this probably sounds a bit over the top and like you'll be fiddling about with your feet every few steps, but if you're going for longer distances than you normally walk, day after day, then be prepared for a few suprises in the foot department and know how to deal with them. Feet swell up a hell of a lot if you're doing long distances so boots that fit great normally, suddenly feel tight after hours of walking and carrying kit.
When you've stopped walking each day, have some lightweight footwear (sandals?) to change into that will let your feet breathe and recover. Wash them and give them a powdering with some antiseptic talc. Keep your nails trimmed too. I lost my big and little toenails on both feet during a particularly challenging trip once.
Use socks with padded areas on the heel and toe and make sure you change them often. Washing your socks will put a bit of 'spring' back into them. You can hang your damp ones off your rucsack to dry while you walk (stops people trying to steal your kit too).
Take plenty of good painkillers and vaseline too - for those chafes and rubs.
The only other thing I would say is to plan your route with regular water resupply points (daily) so you don't have to carry as much.
And leave the hatchet at home.