Preparation in advance, as for all our long-distance walks, was invaluable and, of course, you need to have contingency plans for bad weather and illness. For the GTA we would recommend in particular:
Language - in most but not all overnight stays some English was spoken. French can often
be used but learning a few basic Italian phrases helps ease your way!
Travel - check out on services in advance and asking for local assistance where possible. Our 6-week trek begain in Ormea, a train and bus ride from Turin and finished in Quincinetto in the Aosta valley on the train line to Turin. Although the route is remote and passes mainly through very small settlements at no point are you far from roadheads or towns served by excellent bus or train services.
Money - ATMs are few and far between and may not always work ... and at some of the overnight stays where mention is made in the guide book of accepting credit cards the machines did not work either. You have to be brave and carry enough cash for at least 3 weeks with you!