Hi Kennedy1
There are probably other threads on training strategies that people have used. It will depend upon your fitness already, how far you're walking, and how long you have to do it.
If you're starting at St Jean, you'll have a big climb on the first day. As I planned my trip at short notice and was totally unfit, I just started slowly and chose the alternative Valcarlos route to Roncesvalles, which isn't quite as severe. After that there are a few significant climbs along the way, but if I remember correctly none of them are more than about half a day's walk. The ones that spring to mind are the Alto de Perdon after Pamplona (where the Pilgrim Monument is), a hill just beyond Castrojeriz, the climb up to the cross of iron after Rabanal, and up to O Cebreiro where you arrive in Galicia.
I found that just getting as far as these hills was enough training to get over them. If I was to do some training, I'd just find a fairly modest hill that might take a couple of hours to climb. On the Camino you'll always be on well trodden paths and tracks, so if you find that your training involves scrabbling up a hill with your hands and feet, you're probably overdoing it!
Good luck and Buen Camino!
Keith