When done properly, the bar moves in a perfectly vertical plane only, which is the most efficient path. To do this, one must move the head back to make room for the bar, then replace the head to the normal position after the bar passes by. The lift is complete when the arms are locked out overhead, with the head "through the window". Finally, some other key points to address is the importance of having active shoulders, a strong jump stance with the feet directly under the hips, and unlike the push press and the jerks, there is no "dip" or hip drive to aid in driving the load upwards.
The Overhead Press is one of the nine foundational movements of the CrossFit Methodology.