These are really lovely studies. Great job! Line control comes down to dexterity which is trained with practice. Keep drawing every day and you will see results. Consciously remind yourself with each line to make a long, light, loose and tapered stroke. It may slow you down, but once you incorporate this into your practice, your speed will increase over time. Love Mucha's work. If you haven't already, check out his Le Pater series of drawings.