If you want to get fitter, faster or slimmer, then interval training is the way to go: There is no right or wrong way to do interval training. Almost any formula of high intensity intervals alternating with intervals of low intensity will increase your fitness level in a shorter amount of time than steady state training. (See post: http://wellerbodiespersonaltraining.blogspot.com/2012/06/beware-hiit.html for more on high intensity training). One easy to follow formula is the 10-20-30 plan. You can do this with any type of aerobic training.
Go as fast as you can for 10 seconds, (sprint, walk or pedal your hardest), decrease to a moderate speed for 20 seconds, then maintain an easy pace for 30 seconds. Do this for about 5 minutes, rest with a very easy pace for 2 minutes, and then repeat 3-4 more times.Cool down and you are done!
Try this 2-3 times a week (but not 2 days in a row), and you will see your speed and fitness level increase while your workout time decreases.