I can ask someone to tilt his head back(or left or right or forward), but if I want to ask him to make his head to the original position, i.e. to turn the head upright, can I say "turn your head straight"?
When I was a portrait photographer I faced this situation daily. The problem with "look" is that it can entail changing the position of the head or the direction of the eyes.
I dealt with this by giving "chin" directions. Chin up; chin down, chin to the right, etc.
After I had the head pointed as I wished, I would direct the eyes. I could just say "look up a little" or "to the right a little" but when directed like that the eyes tended to look unfocused. So I would usually direct them to look at a specific point on a wall or at a specific item to draw the eyes into focus.
But if you are trying only to have the subject look at something then "look to the right" or "look up" or "look straight ahead" all work.