Know your group and consider the interests and tastes of all your members. Balance fiction and nonfiction, male and female authors, light and heavy topics. Try a classic, a play, or some poetry.  Sample science fiction or a mystery.

Avoid feel-good books, "nice" books make for short, bland discussions. But don't pick too many books that make you feel angry, sad, or disturbed.

Look for well developed characters, compelling themes, complex issues, and conflict.

Read at least the first chapter of a book before you nominate it for discussion. Is it worth the time and effort your group will spend on reading and discussion?

Don't pick too many long books, many groups complain after 400 pages.