First, note that your mouth has to be opened while brushing. Place your toothbrush at 45 degrees between your teeth and the gum (picture above). Then make a downward motion (like you are sweeping)
|'sweep' the inner surfaces as well using same motion.|
For the teeth in the lower jaw, you will do the same thing.
Brush the chewing surfaces as well.
This is basically what toothbrushing entails. As you can see, its not hard.
Take your time to do it. If you spend less than two minutes in brushing, you haven't brushed well.