The teachers of the Famous Artist's School correspondence course were good at drawing hands, especially Al Dorne, who I believe did these examples.
They had a useful three-step process for approaching the challenge: 1. Gesture, 2. Construction, and 3. Refinement.
1. Gesture. The first pass shows placement and action, using curving or straight lines. This should be sketched lightly so that you can erase it later.
2. Construction. The second pass conceives the fingers as solid block-like forms. Be aware of relative size of forms.
3. Refinement. Add small forms using lighting that reinforces the structure. Don't lose the large gesture and simple forms worked out in the previous two steps.
"It is helpful to think of the hand as being composed of three masses—the palm, the thumb part, and the mass of the fingers."
"The block method of construction is particularly useful in working out foreshortened views of the hand because it is easier to imagine what happens in perspective to a cube than a finger."
"The nail fits into the top plane of the finger and rises slightly toward the tip. Note how the top plane slants downward from the knuckle to the nail."
"You need never be at a loss for hands to study. Even when drawing, you have another hand to serve as a model at any time. If you place a mirror in front of yourself to reflect your free hand you will have an infinite variety of poses to choose from."
Copies of the Famous Artist School binders appear in the used-book market from time to time. The links below take you to a couple sets on Amazon. Make sure the editions of the binders are from the 1950s, as the quality of the drawings goes down in later versions.
Famous Artists Course 3 binder set
Famous Artists Course Lessons 1 - 24
Many of the same lessons on hands (and heads and figures) were reprinted in a single volume book: The Figure: An Artist's Approach to Drawing and Construction