Endurance can come in many forms but the key ingredient to getting faster is Power output which is Force x Speed.  So the more force you are able to produce over a given speed will increase your power output.  The key to power production is training the body to become stronger through proper training.   Below is a workout that combines strength training and bike intervals all into one full body workout.  Depending on your training schedule I like to do this workout about 2x a month on heavy weeks.

Cycling Strength Trainer