Previous training: The Way by walk
Even if The Way of St. James is for everyone, it is vital that you prepare your body for the journey.
You should start your training a few months before you start your pilgrimage, by walking routes that gradually gets longer and more intense. Remember that you have to train your body, so is not going to be helpful to force yourself to do a very intese walk or exercise if your muscles are not ready yet, take your time to train.
Another thing you can do to take care of your body is to visit a physiotherapist and check that your muscles are in a optimate condition, your physiotherapist can also help you by teaaching you different exercise routines about warm-ups and strectches to do along the way, to prevent injuries.
At the start of your march, the rythm should be smooth, letting the body warm-up slowly and then increasing the intensity, but maintaining always a rythm that is not an excessive effort and let you enjoy other activities, like talking with your companions.
Is it also very important that you train in different terrains. You will find very different type of paths along your way, and your body needs to be able to walk confident in different situations, not just in a flat road, but also in dirt, hills, etc.
But don't forget, everyone can do The Way! All you need is a bit of training!