Interval training on an exercise bike or indoor training bike is a great way to increase your cardio-vascular fitness and speed. It will also help you to burn more calories than a regular workout over the same time period. It involves short bursts of high intensity exercise followed by recovery periods. This video also provides an amazing thigh workout to help you tone and strengthen your legs.
Make sure you are in the correct riding position before you start. On most indoor training bikes you can adjust the seat in two directions (up and move it towards or away from the handlebars). You should also be able to adjust to position of the handles so that you are really comfortable. Most cyclists make the mistake of positioning the saddle too low. This stops you from being able to stretch out your leg fully and reduces the amount of power you can exert on the pedal.
This is a 10 minute workout which allows you to combine it with a range of other exercise routines or a longer ride. Start by selecting a very low resistance and pedal for one minute to warm up your legs. Then for ten seconds at the end of each minute you need to turn the resistance up to high. Stand up and pedal as hard as you can for the ten seconds. Then return to the recovery with low resistance riding for the remainder of the minute. Repeat this for the full 10 minute period.