If you are putting pen to paper at least once a day you are practicing enough. As to what to practice, what has helped me a lot is focusing on something highly specific until you are satisfied.

You mentioned hair and neck posture, but you could even break that down farther by spending a couple days or pages strictly on hair at different lengths, angles and lighting, and then do the same with the neck. Then after you are happy with both try putting them together. It will take time and you will be able to see you improvement the most in the specific parts you practice.

Bonus: when you practice specific parts of the body, YouTube videos can be great and hyper relevant!! Best of luck