SHORT, HARD INTERVAL DAYS
To build speed and power, do short, hard intervals. After warming up, go as hard as you can (with your HR in the ZONE) for one minute. During this "on" period, you should ride hard enough to get your HR to peak right at 90% of MHR. Then rest to get HR down to about 60 to 70% of MHR and repeat the interval. Never do hard intervals more than twice a week. Serious riders will do hard intervals (in succession) until they cannot do another one. You should start out with about 4.
HILL DAYS
Get your HR to about 80% of MHR and try to keep it there for the duration of the climb. Never push your HR up to the 90% level for too long on a climb or you will blow up.
EASY DAYS
You should have easy days between your long interval, short interval, and hill days. These rides are needed to help flush lactic acid from your muscles. Easy rides should be over 30 minutes with your HR at about 60% of MHR. Note that long intervals below 70% of MHR are good for burning fat.