Getting a pencil drawing on the watercolor paper is very subjective. Every artist will have their own artistic means or approach of how they do it. Let me give you a few examples.
I use the cheap yellow #2 (HB) pencils nothing fancy. I also like 7mm mechanical pencils for portraits because they are sharper for details. You don’t want a hard (H) light, drawing pencil that you may press too hard and scratch or dent the surface of the paper. 5mm might also be too sharp and leave dents if pressed too hard. If your wish is to not see the line don’t press too hard and don’t use too soft of a pencil, like 4B or 6B. #2 (HB) pencils will smudge but can be erased easily with a kneaded eraser to adjust your drawings. When the drawing is complete, pick up the loose surface graphite with kneaded eraser so it doesn’t mix with your paints.
When I draw lines on my paper I have a few things in mind. First and foremost, “if the line or mark you draw will be seen, make it interesting”! Sketchy lines look artsy! Let them change width and vary from light to dark. You will like the results (message from artist Ted Nuttall workshop).
One technique I am currently using is to make shorter solid type lines for hard edges. Eye lids, middle of lips etc. These lines will be covered by darker paint and will not be visible. I use light dashy lines for the borders of soft edges and similar value parts of the face. The round outside edge of the nostrils, top of the lips, soft shadows, jaw lines, top of chin, cheek highlights, glints, etc. Keep these lines that show soft edge “form shadows” very light on your drawing. When you initially draw them erase them back to very faint before you add paint. On the first washes use these marks to lay in some color. With paint now as your reference the lines are no longer needed. If you don’t need them anymore you can erase them when dry. Note; Graphite will soak in and become embedded into the paper. They should come up if you drew them light and with only one wash on top of them.
If you use some technique to transfer or trace your image onto your paper be very careful not to make your lines boring. Don’t let your lines get too long, too straight, or continuous. These lines are stiff and uninteresting!!! Also, try to keep your lines to a minimum. It is a painting not a drawing!
I hope you found this helpful
Edited: 29 May 2020