You have to get in (2) big rides each month and preferably (3) big rides. Rides that are at least 5-6 hours long that force you to dig deep near the end, so that when you reach home, you are tired and your muscles are quivering(not cramping though) from the fatigue. This is the #1 thing you can do and you cannot skip this step if you want to go to the next level, no matter if you are a pro or a recreational cyclist, you have to increase the miles, hours, and overall volume of training stress in order to challenge your cardiovascular and muscular system enough to create positive adaptations for the future.