Drawing can be fun and profitable. While no one can teach talent, there are certain tools that separate the professionals from the amateurs. One such tool is the French curve. For flowing, consistent curves drawn with a single stroke of your pencil, you will need to use a French curve.
Visualise the curved line that you want to draw. Imagine what parts of your page the curved line will pass through.
Mark four points on your page that the curve will pass through by making light dots on your paper with your pencil. Make sure the dots are light enough that they will not interfere with your final picture, but heavy enough that you can see them for now.
Position your French curve so that a single edge crosses over the four points. You may need to slide your french curve or turn it slightly to find which angle will allow it to connect the four points.
Run your pencil tip along the edge and connect the four points. Remove the French curve to see your finished line.
You can make a line curve multiple times. Each curve requires four plot points and a separate positioning of the French curve. Use a sharp pencil to get a thin line.
Keep your French curve clean to avoid smearing graphite or charcoal onto fresh paper.