Any artist can verify that having a double-sided pen is like having two desserts -- one before dinner, and one afterwards! Most double-sided pens have a thin tip on one end, and a wide tip on the other. Use the thin side to lightly sketch the beginning form of your artwork, and then after you've added some color, use the wide side to ink your drawing with thick, dynamic lines.
You can also use a double-sided highlighter to more efficiently mark your notes! Use the wide tip for key points, and the thin tip to underline relevant supporting points.