Buy good but not expensive editions.

Do not spend on a single costly work, of interest to few and seldom used by that few, a sum that would buy 20 or perhaps 100 volumes that would be in constant and profitable use by many.
Buy no book unless by personal acquaintance, or upon competent and trustworthy testimony, it is worth adding to your library.

Do not feel that you must buy complete sets of an author, or all of any "series"; all the works of very few authors are worth having.

Do not buy cheap editions of fiction; the paper, presswork, and binding is poor, and is simply a waste of money.

The best is none too good in buying fiction, for it wears out fast, and has to be rebound, and then replaced.