Read some more information on the web and get some books on the subject. To any of that I would add the following simple advice. If you get your heart rate up so you are working reasonably hard at a steady heart rate for 15 min or so, gradually increase that heart rate by about 5 beats and hold that steady for another 15 min or so. At some point you'll get to the point where you will be forced to breathe too hard to hold that heart rate. Back off 5 beats and you will be at about the max you can handle aerobically. The tipping point where you move from being able to keep the heart rate up continually vs being unable to keep enough oxygen going to your lungs will be (roughly) your anaerobic threshold. Long rides at about 75-85% of that should seem pretty easy but will maximize your health/aerobic conditioning. You should be able to do that for hours. Occasional spurts at 90-100% of your threshold will also help build your anaerobic conditioning, but for most non-competitive cyclists wanting to get into better health, the key is long times at more reasonable rates of aerobic conditioning.