The problem with sculpting a head especially if the clay you are using is soft is as you sculpt you can end up with a pin head. As you work the forehead and you have to constantly push things back where they belong. One thing that can help is to have a bit more of a solid core to sculpt over. A bit of tin foil or some other solid form so it is not so easy to push things around.
But in some scales this is not really that easy so you just have to keep looking at the sculpt form every angle. Side, top, head on. Just keep looking and make sure you are not pushing it around too much. If you feel like you are not getting it or have just gotten to tired to see it with fresh eyes. Keep a mirror on your desk and look at it in the mirror and things you did not notice will pop out at you.