Reddit reviews Culture Shock! Czech Republic: A Survival Guide to Customs and Etiquette (Culture Shock! Guides)

As far as books go, the Culture Shock and Culture Smart guides are pretty good. The book From Good King Wenceslas to the Good Soldier Svejk is a deeper dive especially into 20th-century Czech culture, but a lot of the references now are more historical (life under communism, etc.) than applicable to contemporary life.

Broadly speaking, Czechs are proud of their culture, but not in any ostentatious way (outside of cheering for sports teams, for example, they're not really into flag displays like Americans).

People are generally reserved until you get to know them, but then they can be very friendly and generous.

People tend to project a somewhat skeptical, "realistic" view of the world, so some Czechs can be dismissive of "grandiose" theoretical frameworks (feminism, the EU, etc); on the other hand, many Czechs enjoy traveling and appreciate different cultures. Education is highly valued.

Most people aren't religious, and those who are are usually low-key about it. The only time you're likely to hear references to Jesus in a typical day would be when a middle-aged lady exclaims "Ježíš Maria!" or "Pane bože" (which sound much milder in Czech than English).

Many Czechs like to complain, but they also have a great, kind of dark or absurd sense of humor.

A lot of Czechs love nature, gardening, going for hikes, swimming and so on.

I think the biggest mistakes I might see a fellow American making would be labeling the country "Eastern Europe" (it's "Central Europe"), only talking about how cheap the prices are, being too informal in certain situations (i.e. wearing shorts to the opera), bitching about the inevitable cultural differences, and speaking too loudly in public. But Czechs also generally have a live and let live attitude about things (although they might privately grumble), so don't be too self-conscious.