Curved lines — and straight lines that are not perfectly vertical
or horizontal — will show some degree of jaggedness on the screen. When printed,
the curves appear smooth.
You can choose Curve to
draw precise curves.
You can choose Freeform to
give your drawing a smoother look than choosing Scribble.
Try increasing the magnification by zooming in. It's
easier to draw details at 200 percent.
Try setting your mouse to the slowest tracking speed available. You have
greater control when you draw at a slow speed.
You can adjust the shape of freeforms to make them look smoother. Select and
right-click the freeform, click Edit Points to make its points or vertices appear, and
then drag any point. Be sure to increase the magnification in the Zoom box to 200
percent.
You can smooth freeforms by removing individual points. Select and
right-click the freeform, and then click Edit Points to make its points appear.
Position the pointer over the point you want to delete, and then press CTRL as you click
the point.
to
draw precise curves. 
to
give your drawing a smoother look than choosing Scribble 
.