Well the recommended amount of sleep varies from person to person, as factors such as age and sleep patterns come into consideration. Generally adults should look to get between 7 to 8 hours of sleep every night, whereas teenagers, children and babies vary even further with recommendations of at least 8 hours a day for teenagers and up to 15 hours a day for babies.
Keeping regular sleeping patterns can help you sleep every night for longer, as well as relaxing before going to bed and avoiding stimulants such as caffeine and alcohol. However I always the find the best way to increase that amount of sleep your receive can be found in your bedroom.
Keeping your bedroom dark helps to keep out the natural light when the sun rises, and a comfortable mattress makes getting out of bed a chore so if you do happen to wake up early then you may just find you fall asleep again quickly if you are comfortable.