Perhaps it would be worthwhile to consider the Five Laws of Library Science of Dr. S. R. Ranganathan as the basic guidelines for formulating the objectives/policies and procedures for document selection and procurement. Ranganathan's first three Laws of Library Science are helpful in formulating the principles of document selection.
The First Law -- Books are for use - makes it obligatory that only those documents should be selected which are of use to the clientele of a particular library. While selecting the documents, the present and potential requirements of the users must be kept in view. A school or public library should avoid the selection of costly books which are not likely to be in frequent demand. For a children's library, the books should be illustrated in bold typeface and attractive.
The Second Law of Library Science - every reader his for book - directs the selector to cater to the informational needs of all the users of the library. The subject or the language or the style of exposition of documents to be selected should be in accordance with the requirement of the users. This is possible only when the selector of documents knows the users and their requirements well.
Ranganathan's Third Law of Library Science - Every book its reader - suggests that all efforts should be made to put to use those documents of value which have been selected in anticipation of the needs of the users.