I have a really simple drawing tip for drawing on toned paper with two colors, but in order to explain it, I'll describe my whole drawing process from the beginning so you know what I'm talking about. It's not as complicated as it appears.
1. Start out with loose faint marks to position the drawing on the page correctly. Try to get the whole subject on the paper. You don't have to fill up the whole sheet of paper, but maximize your use of the paper.
2. Make loose, faint construction lines of big general shapes: oval for head, column for neck, etc. Draw the movement of the shapes in faint lines: for example, a kneeling figure is a big C. I always think of this stage as the "Big Picture" phase, to remind myself to see the Big Picture.
3. Indicate the midpoints of the body - synthesis of the pubis for the body; the eyes for the head. Make sure that the various axis lines are correct: the axis lines running through the eyebrows, eyes, nose, lips, chin should be parallel. Check the shoulder, breast, hip, knee and ankle axis lines - are they doing what the model is doing?
4. Now you can start to draw: contour lines, shadows, background
5. Define the bony landmarks: anatomical details are important. Accentuate the big masses. Find your darkest darks, being careful not to lose your mid tones. Establish all the values from lightest light to darkest dark. Don't overwork your surface!
6. Hit the highlights - the last little touches of light that bring the whole drawing into dimensionality: tip of the nose, forehead, eyelid, eyeball, lips, etc. Don't over use your whites!
7. OK, here's the tip. Everybody knows about highlights. There's also the inverse of highlights, but "dark lights" makes no sense, so I think of them as "a thousand points of darkness", although it's not a thousand, but more like a few dozen. These are tiny little points of darkness, usually triangular, that occur when there are several intersecting shapes creating shadows. You don't ever want to make stripes of shadow running down the arm or leg, whcih flattens the forms and wrecks everything. Instead, create the illusion of shadows with a thousand points of darkness.