My own schedule: dentist checks every year, cleanings every 6 months.
Regularly getting your teeth cleaned professionally is important! A hygienist doesn't have the training a dentist has, but he/she can screen for things like broken fillings - and of course, gum disease.
I don't enjoy the time I spend getting cleanings but I do it every 6 months.
Personal observation: yes dentists will sometimes try to sell you services. Some of my friends follow every recommendation their dentist says - and, frankly they tend to have nice teeth. Some take the "Meh, he's just trying to sell me stuff again" route, and they tend to have icky mouths. I try to take the middle road.