Remember Library of Congress Subject Headings are being added to and subtracted to all the time. It shouldn't happen, but obsolete terms may be floating around our catalog, OCLC or even LC. Please look for an authority records when you decide to use a heading.
Some material get no Subject Headings
Fiction The Bible and other sacred texts
The subject heading should be as specific as the subject of the entire book
Assign a specific subject when available or create the concept using subdivisions and multiple headings.
Only create subject headings for concepts that represent more than 20% of the work.
The first subject heading usually matches the call number for the work. Subject heading creation and call number creation should happen almost simultaneously.
Some titles are much easier to assign subjects to than others. That's life.
Look at the Object in hand Often the subject heading is easy to identify simply because an author will title his work to reflect its main content. Additional clues can be obtained from the preface or introduction to the work, where the purpose of the work is discussed by the individual most intimately acquainted with the content. Next in importance is the Table of Contents where the logically arranged work will present an outline of content. All of these are valuable clues as to the appropriate subject access points to be included in the metadata.
Specialty works require some introspection to ascertain the appropriate subject headings; exhibition catalogs, conference publications, biographies and autobiographies have individual quirks associated with them, but all are easily categorized after recognition of their special character has been accomplished. (See below for further issues regarding call numbers for these.)
Science and technology can be a challenge for subject heading selection. It has been observed that, thankfully, vendors of books in this area do seem more inclined to provide subject headings. If not, and you are unsure about subjects in this, as in any area, ask for help.
LC's Subject Cataloging Manual, H180 says to assign headings for topics that represent 20 percent or more of the work. A maximum of 6 is appropriate, LC practice is to assign no more than ten.
Once the subject(s) has been identified, the next step is to find the appropriate LCSH for it. In the cataloging module do a Builder search with subject key words. This should bring up titles with subjects similar to yours. Examine these subject headings.
Place names should also be authority verified and entered. If a place is not in the geographic name authority, use the next larger geographic entity that is verifiable unless the name is so important for access that to not use it would hinder the user. Similar considerations apply for the names of persons who are the subject of a work. Our local records will contain some places and names without proper authority. Normally, three subject headings and the additional place or person names are appropriate for full level records. More can be used if needed, and sometimes one is adequate. This is a prime example of the proper use of cataloger's discretion.
Creating subject headings is an art based on the experience and knowledge of the cataloger, as well as the compositional capabilities of the author. Different catalogers will select different subject headings for the same work. The important consideration is user access. This issue should be foremost in the mind of the cataloger when subject headings are created for a work.