The most critical mistake when drawing anything is... drum roll... drawing it too big, zooming in too much, and losing the overall shape.
Watch masters work on thumbnail-sized portraits.
That is how you do it.
If it works as a thumbnail, it will usually hold up as a full-size portrait.
Three rules to ingrain in your stubbornly stupid mind:
- Start small.
- Proportions matter.
- A good head shape beats beautiful individual facial features.
Look at the head shape.
That is your canvas.
If it looks awful, start again.
Do not waste time putting in features.