The advances in short-run digital printing now make it easier than ever before to produce printed books in a viable and economical way. Books can readily be ordered in small, manageable quantities, and the finished copies are now as professional in appearance as those produced by more traditional litho print-runs.
It's also possible to set up Print-on-Demand (POD) for a book, whereby copies can be ordered, printed and despatched on demand - even as a single copy. However POD does have a significant bearing on the necessary selling price, so the decision on how to print will vary from title to title.
It may still prove most effective to produce a book by a conventional litho print-run, which can generally come into play from a few hundred copies (dependent on the format, etc.). But often an initial commitment to a short digital run of perhaps 100 to 300 copies is preferred.
There are numerous different sizes and formats in which books can be printed, with the most popular shown below. Generally the format will be suited to the genre.