Some people ride themselves into shape during the first couple of weeks of a long tour. I prefer to begin in pretty good riding shape, but I ride quite a bit for enjoyment, so I don't do too much special training.

I would recommend loading your bike fully and riding it regularly for the week or two before your tour. Not so much to get you into shape, although it will help do that, but to test everything for tightness, balance, and maneuverability.

For most bike tourists, the tour itself isn't enormously strenuous. If you plan to ride 60 miles in a day and you have all day to do it, it's only six hours on the bike at 10mph. Three hours before lunch and three hours after lunch and you're at your daily destination by early afternoon. Some days are longer and hills or a headwind will make you work harder. Touring is more an exercise of persistence than feat of athletic ability.