Whatever your reasons, getting involved in some form of basic training is worthwhile. It will usually result in you being able to ride further and with less effort. Using a heart rate monitor (HRM) is useful as it prevents you from overstretching yourself.
If you're out of shape and/or just getting started in cycling, begin slowly. Your initial rides should be 20-30 minutes in duration, perhaps 3 times a week. Concentrate on pedalling briskly. As your fitness increases, ride 5 days a week for at least 30 minutes and then gradually add more time, but no more than 10% per week.
Every cyclist can benefit from a structured weekly programme that includes both speed and distance training. Whether you objective is to firm your legs, lose weight and be healthier, use a programme which contains the following:
Moderate days - to lose weight, ride medium distances at a comfortable pace. This will burn fat, as opposed to the carbohydrate that fuels short, intense efforts such as charging up hills.
An endurance day - to improve your stamina, do one long ride every week. Again don't worry about time, just complete the distance.
The above are usually more than adequate. However, if you want to ride further, faster, or wish to develop the ability to quickly accelerate, you need to do a "speedwork" session once a week. This is a training session based of a warm-up followed by several bursts of all-out effort mixed with easy riding for full recovery.
Take your time warming up for this workout. For example, it may take 20-30 minutes of easy riding before you feel ready to train hard. Stretching can often help reduce this time.
As indicated, do one day a week of speedwork and perhaps one of intervals (never back to back). Both these sessions are especially beneficial for cardiovascular improvement and muscle tone.
Rather than take the day off after a hard effort such as the above session, take an easy ride, called "active recovery". Use the opportunity to cycle with family and friends who are normally too slow for you. A day off training refreshes your body. Always have at least one day off per week. Use the time for bike maintenance.
Don't get bored by riding the same training route. Have numerous routes and ride them in the opposite direction occasionally. On your long endurance rides, throw in a couple of sprints every 45 minutes or so. You'll relieve saddle pressure, stretch your legs, add some variety, and develop speed.