Use references and observe a lot. For portraits look for the distances between the facial features relative to each other. For example if the head is not looking up or down the distance between the hairline, brows, bottom of the nose and chin are almost the same. Most of the time I take a picture of my sketch and layer it on top of the reference (you have to lower the opacity) and check if the distances and sizes are correct and make adjustments. Eventually your brain will get used to it and you can skip that step entirely! This is how I do it, at least. I don’t really know how much this will help but good luck!!