Running form has been a hotly debated topic for many years. When I went to school we taught everyone that you should strike the ground with the outside of your heel and move through your midfoot and leave the ground off your big toe. This is the correct way to walk, but many believe that this is not an effective way to run. Personally I believe that the fast your move the further up your foot your contact with the ground should be. Think about a sprinter getting ready to explode off the starting blocks, they are on their toes and will continue to run that for the duration of the race. Another way to see proper running form is to look at someone who hasn’t lost their innate running form, a five year old. Kids never run on their heels, they are always on their toes are midfoot when they contact the ground.
I believe the Good Form Running folks did an amazing job of simplifying a very complicated topic into 4 principles which are in the videos below. They also created a Good Form Running PDF that summarizes the main points of Good Form Running.