I came across a great article on building your endurance on the bike from Bicycling Victoria's website and thought I'd pass along thier great insights.
 
Written by Bicycling Victoria

Once you feel comfortable with the basics, you may feel ready for preparing for longer rides. Bicycle Victoria offers some sound and simple starters to increase your distance.

What to expect from this guide

• How to stay comfortable on longer rides
• How to eat and drink right
• How to look after your body
• A training schedule for endurance training
• A list of other, more specialised resources

Getting the basics in order

Before launching into endurance riding, we recommend you ensure you've got the basics covered. Read the Bicycle Victoria web page 'Basic and beginner training' first for information on:

• The right clothing
• The right gear
• The right skills
• The right food and water
• Initial check
• Warm ups
• Basic riding skills
• Building up slowly and frequently
• Training with others
• Training rides

 Maintain fuel levels

• Use a 'Trickle feed' system - eating and drinking small amounts regularly. Drink every 10-15 minutes and eat every 20-30 minutes. A countdown alarm feature on your watch will assist with the timing.
• Don't consume large meals whilst cycling, as more blood will go to your stomach, weakening your legs and causing indigestion.
• Good fluids are water, along with Gatorade, milkshakes and vegetable juice.
• Bananas, apples, sultanas, dried apricots, fruitcake, sandwiches, vanilla slices and meat pies kept the legs turning!
• Too much plain water can increase your chance of developing hyponatremia or depleted salt levels in the blood. Electrolyte products like Gatorade (or cheaper to buy Staminade in powder form) will ensure salt levels do not deplete.

Staying comfortable

• Prevent saddle sores. If you have trouble with a rash or boils from sitting on the saddle too long, try washing the problem area with a products such as Betadine Surgical Antiseptic Scrub, T-tree, lavender or eucalyptus oil before and after cycling. Betadine is a bactericidal, fungicidal and virucidal cleanser, and is available from the chemist. If you are unsure about the use of any of these products, seek professional advice from a health food store, pharmacist or doctor.
• Change your knicks (bike pants) every 6 hours, especially in warmer weather. If you get sore try a variety of nappy rash creams or be patient and wait a couple of days for your hide to thicken! Try using a gel seat cover.
• Male and female cyclists should use gender appropriate bike knicks. For women there are special 'ladies knicks' and special women's saddles, designed to suit the female anatomy.

Look after your body

• Nothing can save your knees if they become painful. Knees are usually sore during the first couple of hours back on the bike in the morning.
• Cold weather makes them worse. Keep your legs rolling over, but don't push huge gears. Wear long knicks or leg warmers. Check your seat height and body position. Try altering your seat or handlebars slightly.

Look after your mind

• Fatigue and loneliness. It's important to evaluate yourself throughout the day, hour by hour, as conditions change constantly.
• Keep alert by concentrating on your goal - the distance you intend to achieve each day. Keep positive images and words rolling along with your wheels. Concentrate on strong, powerful words.

Endurance training rides

• A local cycling group might help you with your training program.

• Once you are feeling comfortable on your bike and have built up the weekly total, include some hills on your training ride. Find a long steady climb and constantly ride it, changing gears to match the hill.

• On hills, use your gears and change down. This will build up strength that you will need when you start riding past the 70km mark.

• There is no need to stand up on the pedals. Riding hills sitting in the seat is more energy efficient. You can stand up for short sessions (say 50 metres) to stretch the legs and give your bottom a rest.

12-week 'Consistency Programme'

Week	Longest Weekly Ride	Other Weekly Rides	Total Distance
1	35km	25km, 20km	80km
2	40km	30km, 25km	95km
3	45km	35km, 30km	110km
4	50km	25km, 20km, 20km	115km
5	55km	30km, 25km, 20km	130km
6	60km	30km, 30km, 25km	145km
7	60km	30km, 20km, 20km, 20km	150km
8	65km	30km, 20km, 20km, 15km	150km
9	70km	30km, 20km, 15km, 15km	150km
10	70km	30km, 15km, 15km, 15km	145km
11	75km	30km, 30km, 20km, 15km	170km
12	75km	30km, 25km, 20km, 15km	165km

Books

Base Building for Cyclists

Source: http://www.bv.com.au/bikes-and-riding/10433/