To cycle 100 miles, follow the 80:20 rule where 80% of your rides are at a low intensity and 20% are high intensity to avoid overtraining. Also vary your rides to work on different skills and improve in areas like hill climbing or speed. Be sure to eat throughout longer rides, snacking on energy bars or peanut butter and jam sandwiches to maintain your calories burned. Finally, prepare mentally for the challenges you may face, using techniques like visualization to handle difficult periods where you want to quit.