There are a number of this that you could do to smoothen up the lines in Procreate:
- You could draw the lines using your shoulder’s movement rather than drawing with your ankles. It gives you more stability, makes extra room for arm movement and gives you the straight lines.
- You could adjust the Streamline slider, by going in brush’s setting and setting the streamline to its maximum value.
- You could use drawing gloves for smooth movements.