Techniques to increase average cadence for endurance-riding?
If you want to change your cadence, just change it. Take your cruising gear on your bike and calculate what your current cruising cadence is. Let's say you usually cruise at 16mph and your typical cadence is 75. If you want to be at 90, go into a lower gear and try to keep the same speed. This will increase your cadence.

The benefit of a high cadence is that the higher the cadence the more aerobic you are (more cardio, less muscular). This will naturally increase your lung capacity providing increased stamina at any cadence because your vo2 max (google this) will increase with regular cardio sessions.