Hey Bev, you're not alone!
We all have to keep experimenting and practicing.
When working from life, I found that having a strong light source and changing its position sometimes helps to find the planes.When I can't do that I walk around the model (without disturbing the others too much as I can't afford to pay a model on my own).
When working from a photograph, we are much more relying on our constructive knowledge. therefor it helps to quickly sketch the planes of the head (or any body part for that matter) first on a piece of paper. I do this with ballpen or a fine marker. These thumbnails also help to establish an interesting composition as especially when working small, it can be interesting to choose not to depict the complete body of the model.
Hope it helps and thanks for motivating me to continue to experiment, Bev.