Now that you've gotten used to your bike, it is all about cadence and pedal stroke. You want to shoot for 75 – 100 RPMs on the pedal stroke to maximize your workout ability on a bicycle. Don’t exceed 100 though, the effects from some reason dwindle over 100.
You also want to learn how to pedal through the pedal cycle, not just push down with one leg then the other. This takes a lot of practice, and thought when you are doing it in the beginning, so I would recommend practicing this on a stationary bike at the gym. Once you get this down along with a good cadence, you can really get a killer workout ok the bike.
If you really want to get into it, you move on to including Lactic Threshold training and Max Vo2 trailing.