A neutral head position is one of the key focal points for freestyle swimming in my swim book- Simple Swims: practices for balanced stable swimming.
Keeping the head in line with the spine to help maintain a horizontal body position while swimming. Let the neck muscles relax, nose points down, as though the forehead is on a massage cradle-if you've ever had a massage!
To have a neutral head, it is also key to have good spinal extension in the thoracic spine-the portion of the spine between the shoulder blades. The back of the head, shoulders and hips are just at the surface, arms slope down, gently flutter kick. Gently blow out bubbles, then stop and stand up when needing to breathe in.