I will leave all the detailed responses to the many who train scientifically but in general, spend most of your time spinning in lower heart rate zones, to build your capability to burn fat for fuel, not carbs. this will help you race faster, in the long run (or ride). mix in some hard rides or intervals (maybe hill repeats) once or twice a week. seems like your leg strength is better developed than your cardio capacity (meaning you have a limited cycling base). check out The Cyclists Training Bible by Joe Friel, or Base Building for Cyclists by Thomas Chapple.