Changing brush heads regularly makes a big difference, too. Three days after I change mine, my teeth feel like I just came from a dental cleaning.
Most of my dentists have recommended that I change them every 6 months. I change them and the batteries every 4 weeks.
You also have to pay attention. I just changed dentists and there were gum problems with the back tooth in all four areas. Next time I brushed, I noticed that I was not quite reaching that tooth. Fixed that.