It’s not nearly as difficult as you might think. In France, the route is called the GR 65. It starts in the town of Le Puy in France, and it ends in the village of Saint Jean Pied de Port, where the next route, the Spanish route, begins. That route goes over the Pyrenees to Roncesvalles in Spain, and then across the top of Spain, through the Basque area, through Castile, and, finally, through Galicia. The entire path is well-signed. There are usually other pilgrims around, although, surprisingly, especially in France, many days you don’t see anyone at all, after you leave your night’s shelter, until you get to your midday meal.
There are many sources of information on the Internet. Probably the best one-stop shop is The Confraternity of Saint James. It has a great online library, bookstore, and information. To get a sense, though only a sense, of what walking on the pilgrimage is like, the movie, The Way, is fun to watch. For French readers, there is a great “site of sites”: http://www.chemindecompostelle.com/Liens/Liens.html
There are many guide books. In France the best are the French topoguides for the GR65; the Miam Miam Dodo provides complete information on places to stay. For Spain, it’s hard to say. Gitlitz and Davidson’s The Pilgrimage Road to Santiago is wonderful for its photos and detailed information on the history and art of the route. The more adventurous pilgrims simply set out and walk until they’re tired, trusting in Divine Providence for their meals and shelters. The more middle-class and less trusting make reservations, which is easiest by phone.
The most important thing, by far, is to carry the lightest pack possible. This has always been the warning to the pilgrim. You should be able to weigh in at twelve pounds, before food, drink, and literature, but after cutting all the tags out of your clothes and off your pack, and carrying only a small half-tube of toothpaste.