It is some kind of adventure. But we need to be careful about how we prepare ourselfes for this adventure so that it does not turn into misadventure.
Few important things individuals shoud note is listed down with explanations.
Health:: Health of the person going for this extreame activities should is good. we should have adequate stamina and muscle strength to overcome the daily stress. Note the delayed onset soreness of muscles.
If muscles are worked out more, then muscle tissue tear out and now it is damaged and needs some time to heal. Healing time can go as high as 3-4 days. But then do we have that many rest days when we are on hiking activities or cross country trekking activities? If it is one day activity then you have subsequent days for healing of the muscle. Now wthat to do if you are going for trekking of week long?Best way is to hit the gym and work out your muscles. if you can hold 6kgs on your back and climb verticle for 10 minutes then it is good enough. but if you cannot then it's a time to start the exercise right away. If you need to be in good shape then running for 2kms with good leg excercise is all that is required.
Hamstring curls. 
Smithy
-- Foot care First of all study the terrain you are going to venture. puddy kind of the tropical forest you need good light shoes with ankles. For show you need good hard and protective shoes with ankles and grooves. for regular hiking walking shoes are good enough.
-- Cloathing It is good to take light track pants for any kind of hiking activities. You need to be light. Avoid jeans and any other fancy stuff. Good pair of long sleeves T-shit is good for you. Going in the cold places you can pair of thermals while sleeping. You will not at all require any protective gear while walking uphill in cold places. Your T shit and good jacket is all you require. Yes some people will need an extra layer but that's all. if you are in thorny bushy areas then it is advisable to go with long sleeves T-shit.
-- Gloves & mufler Hand needs to be protected if you in cold areas. Pair of gloves are essential. in cold places your hand will feel lot of chill. At the same time your ear will feel lot of cold. you need someting to pretect it. sometimes jacket hood is helpful or else you can keep a monkey cap ;)
-- Body care when you are in outdoor direct rays of sunlight gives sunburn. take good amount of waterproof sunsceen. SPF 60 and above will do for anyone.
--Hydration Apart from this one need to maintain body hydration level. In cold places you don't feel thirsty, if not hydrated properly then dehydration is big killer in those terrains. it is good Idea to get one camel pack for water. It comes with 2 liter capacity.
- Backpack:: Try to buy good technical rucksack. lots of them are available. I think sport shop people can guide you better on this. Try to buy with good lumber support, that's all you need.
