Brush the outside of the teeth, inside the teeth, your tongue and the chewing surfaces and in between teeth. Using a back and forth motion causes the gum surface to recede, or can expose the root surface or make the root surface tender. You also risk wearing down the gum line. It should have a long, wide handle for a firm grasp. It should have soft, nylon bristles with round ends.
Some brushes are too abrasive and can wear down teeth.
A soft, rounded, multi-tufted brush can clean teeth effectively. Press just firmly enough to reach the spaces between the teeth as well as the surface. Medium and hard bristles are not recommended. It might be a good idea to brush with the radio on, since dentists generally recommend brushing 3-4 minutes, the length of an average song. Using an egg timer is another way to measure your brushing time.