That is a good book.
Before going any further, it is useful to come to a clear understanding what you and others mean by "contrast".
In the context of controlling and using film, contrast is not what sometimes people think of.
I'm speaking here of black and white negative films.
Contrast is a measurement of how films respond to varying amounts of light.
For example, a subject with several adjacent details of similar but not identical tones will render in various ways in a negative, depending on how the contrast in that negative is controlled. We can say that:
1) a film developed to a low contrast will render two adjacent but similar details in almost identical tones;
2) a film developed to a moderate contrast will render two adjacent but similar details in moderately different tones; and
3) a film developed to a high contrast will render two adjacent but similar details in distinctly different tones.
If contrast is too low
for the subject and the light that illuminated it, the result will, at least at the negative stage, be somewhat "flat" or maybe even muddy.
If contrast is too high
for the subject and the light that illuminated it, the result will, at least at the negative stage, be somewhat "harsh" or maybe "sooty".
The tool used to depict the contrast behavior of film is a graphed curve, which shows light level on one axis, and film density on the other axis, and is usually in logarithmic units. Typically the resulting curve is somewhat S shaped, with a middle, relatively straight section. The slope of that straight section is measured, and that slope is a measure of the film's contrast - a steep slope means very contrasty, while a less steep slope means less contrasty.
Here is a couple of examples - from the Kodak datasheet for TMax 400:
The tools used to control that slope, and through them the contrast behavior, include the following:
1) choice of film;
2) to a certain extent, choice of exposure level;
3) choice of developer;
4) dilution of developer;
5) temperature of development;
6) length of development time;
7) nature and extent of agitation.
Assuming a general purpose and commonly used film and developer pairing - which is where I would suggest starting - it makes most sense to give the film normal exposure - which comes from the ISO speed and a working meter - and to use a standard dilution of developer and a standard form of agitation. From there, the variables that are best suited to control the results are the temperature of development, and the time of development.
In both cases, increases will mean increased contrast.
The film and developer manufacturers give good recommendations for where to start. Use a reliable and consistent thermometer, and adjust to get the results you need.
But before you make adjustments, do your best to get help evaluating your results. For many relatively new to this, their perception of what is a "good" negative leads to under-exposed and over-developed negatives. When you see the results from more experienced photographers, you may find yourself surprised how they look different than what you originally supposed.
Here is an example, which I have frequently shared. The light was both dim and relatively low in contrast. The developed negative looks incredibly thin and might lead you to the conclusion that it is too low in contrast. I have scanned it, and I have printed it in a darkroom. I'm happy with how it renders:
I hope you find this helpful.
