I have been reading Margaret King's book "An Artist's Handbook: Materials and Techniques." She has a lot of information about drawing and drawing materials. This is some of what she has to say.
"Draw to study, record, express, and clarify your ideas as you engage in a direct and spontaneous medium."
"Since the Italian Renaissance; drawing has implied spontaneity and has been regarded as the embodiment of artists' ideas, free expression, and the foundation for training in all the arts... It now encompasses a broad and deep range of expression...The function of drawing changed significantly in the 20th Century. Some artists persisted in their exploration of the observed world, while others favored abstraction and nonrepresentational imagery."
"Great painters have always been great draftsmen."
"Ink--for fine-art practices, it is advisable to use inks that are a compound of pigment (not dyes) and shellac to ensure that they are lightfast and durable. Manufactured india inks are made of carbon-black pigment ground in water with shellac, which makes them water resistant. Lightfast in normal indoor light conditions, they can be applied in washes with a brush or with pens such as steel pens with a variety of nibs, crow-quill pens, feather quill pens such as turkey, goose or swan and reed or bamboo."
"Drawing inks may also be bound with acrylic, and they will dry water-resistant."
Of course there are many, many pens on the market today that use lightfast inks such as Sharpie, Micron Pigma, Faber-Castell Pitt pens, etc.
One of Ms. King's "exercises to encourage seeing and drawing:"
"While observing drapery shade by hatching and cross-hatching with pen and ink to show the gradation from light to dark."
You will need to train yourself to see "in" values--not just the darks and lights but also the subtle variations. The more you draw, the more obsrevant you become and seeing values becomes easier. The more values you see and draw, the smoother the transition from dark to light and light to dark areas.
Many people don't understand how important it is to have a full range of values in a work of art. They make the mistake of showing only two or three values very close to each other in range which results in a very dull, flat work. Handling values properly will give depth and dimension to your work that you can't achieve any other way. You will also become a much better artist in other mediums you choosse to work with when you have mastered the use of values. A painter once said that if you get the value right, the color is usually right.
I have a friend who is a painter and he really didn't understand values until 2 or 3 years ago. It has made all the difference in his paintings.