Tooth decay is caused by acids which are produced by bacteria in the presence of sugar. To prevent decay these bacteria, sugar and acids must be periodically removed by way of brushing and flossing.
Generally speaking, a soft bristled toothbrush is best. Whether you use a manual toothbrush or an electric, anything harder than soft, is too hard. Stiff bristles may give you that clean feeling, but they can also abrade your teeth and cause gum recession.
Floss is cheap, so don't be stingy! Tear off about a forearm's length to start. Wrap one end around the middle finger of one hand to "anchor" it, and pick up the other end about 4-6 inches away with the middle finger of the other hand. This allows you to manipulate the floss with your thumb and fore finger. As you soil a section of floss, "reel" in another 4-6 inches of clean floss with the anchor finger as you release the floss with the other finger. Once you get the floss past the tooth contact, move the floss up and down, perpendicular to the tooth. Never shoe-shine the teeth in a back-and-forth motion! You will either notch your teeth or cut your gums, or both!
For most people, a checkup and cleaning every 6 months is standard protocol. Depending on a person's dental health, however, a dental cleaning every 3 to 4 months may be recommended.
For most people, a complete radiographic survey should be done every 3 years, and a "check up" or "recall" set every 6 to 12 months. A complete set of x-rays is estimated to expose you to the same amount of radiation you get on a flight from San Francisco to Seattle.