Many people think that looking straight down is the correct head position while swimming but this is not always the case. Head position affects an individual's body position while swimming so what suits one person may not always suit another. Below is a sequence of head positions to try the next time you are at the pool. Try the full sequence while swimming a length and see what works best for you and then put that into practice on a consistent basis.
Head position 1 - looking straight down with the head under the water
Head position 2 - looking forward at the bottom of the pool approx. 1m
Head position 3 - looking forward at the bottom of the pool approx. 2-3m
Head position 4 - looking almost straight ahead. You should be able to see the end of the pool quite easily in this position. This is the position that Ian Thorpe used back when he was setting world records in the pool.