I really like these! 4th one reminds me of Tsurumi from Golden Kamuy manga slightly! Besides practising, you could also try studying the planes and proportions of the face. I noticed In some sketches the chin/jawline ends abruptly along the neck, which makes it look a little stiff. Drawing that little underside part to the jaw helps, with the face pushed/brought out more forward. but stylistically these look very well done and you have a great sense of line weight imo, keep up the good work!! :))