We walk throughout the year with the local Ramblers group so we consider ourselves 'walking fit ' however we know this is a challenge in every sense of the word. It's 9 days, one after the other. It's longer distances each day than we normally walk, up to 13 miles on 2 days. It's early starts each day which comes as somewhat a shock....now we are retired! Stamina and endurance are the two main attributes but if it's enjoyable along the way you soon forget until you sit down in the evening and take off your boots! This brings me nicely to boots, socks and the essential Compedes. 
Good worn-in boots with plenty of ankle support and nice new comfy socks will do the trick! Compedes for foot sores and blisters are brilliant. I don't get any commission on these, but insist by brand-name and not the generic imitations even though they will be a third of the price. Same detail for clothing, layers and wicking material, cover-ups for arms if it gets too sunny or chilly, Wet-proof tops and bottoms of the light weight pack-away variety. Sun hat, sun cream etc. etc. You know by now that England is changeable 30C - 10C is the norm these days in June! Watch the daily forecast to give you some idea of what you may be able to leave out or take on a particular day. Shorts or long trousers, the jury is out! Ticks are known to inhabit this countryside but the choice is always yours but definitely, don't forget your tick-remover tweezers. Food, as much as you need for the day plus snack energy bars. Water and energy drinks, it's a pain to carry but water taps are few en-route and remember to stop frequently and re-hydrate unless you have one of the built in to your rucksack variety. Rucksack/day-sack of 25/30 litres should do, not too big you are tempted to take the kitchen sink with you, not too small that you cannot fit in all your essentials in for the day. We love pubs but we generally wait until the walk is over before alcohol is taken. This all stems from an incident in France involving bikes, beers, 20 miles back to the hotel and a strong head-wind......perhaps another story for another day?
We have been to the Footprints 'briefing' but as we walked last year it was not 100% essential as we remembered most from last year and the booklet sent to every walker gives plenty of detail and tips. If you are new and live fairly close by.....then do go as it's a chance to ask questions, discuss the pick ups and look around the hall to see who you may meet on the walk. They will tell you there are always back-markers of the red-shirted variety to contact should something go amiss on the walk.
Training: Keith & his team at Footprints can help with this but last year we personally started to walk some longer day-walks leading up to the South Downs Way walk. This just gave us confidence but as we have already said above, we do do Ramblers walks most weeks of around 8 miles.....then the pub! I don't think anyone would embark on a walk of this nature, this distance with ups & downs along the way, without being a walker already but I am sure it has happened!
We worry more about keeping our fitness before and during the walk. Aches and pains are the norm but dodgy knees, hips, ankles, feet and toes have all left a mark on our bodies over the years with any one of these that could cause, at the very least, discomfort and at the worse may stop you continuing. Its not an embarrassment to admit defeat and as long as the team at the pick up point, know you can't make it that day, no harm is done. Sometimes a day or two rest will have you back in your boots before you know it.
Walking poles; we do, some hate them but a lot love them. If you use them it can take a lot of weight off your knees but remember there will sometimes be people around you, so don't leave points sticking out when you are manoeuvring a gate or over a style.......oh and don't leave them behind when you stop for a break. ( yes I have!)
The week before and we get in several long-ish walks around Wendover Woods and plan to walk around 7 miles near Hurley the day before the walk! ....well it was a Ramblers day. We stock up for our Sussex static with 'power' drinks for each day, nibbles, Compedes and pain killers. That should do it, just bread rolls needed for each day. The warm weather thankfully has subsided back to a more 'walkable' temperature we hope.
I have 'invested' in some new mapping software from OS and are already worrying Lesley with the amount of time out of my day I spend in plotting, downloading, transferring and just generally, gazing at the new found digital marvel of technology. 
Already I have loaded onto my mobile the 9 days routes with the SDW highlighted by a thin red line. Is it a touch too much information? Especially as we have walked the route before, albeit in the other direction, and I have last year's walks paper map and its is clearly way-marked all along the way.......but anyway I have bought it, so I am going to use it! I do hope this new toy does not turn me into a distance nerd, you have probably met them, they argue at the end of the day about the point-something of a mile difference between what it says in the programme and what it says on their gadget or what it says on someone else's gadget! Instead of discussing the ups and downs of their wonderful day's walk they all huddle and compare their GPS accuracy, lost signals, low batteries and out of date software etc. This apart, we really are looking forward toFriday and nearer the time will check out what weather the MET Office have instore for us and possibly adjust our backpack contents slightly!