The first book I wholeheartedly recommend is Evidence Explained by Elizabeth Shown Mills.
The author has created a comprehensive website which offers many examples and explanations for citations for a variety of source material.
The second book that I recommend is by a fellow Guild of One-Name Studies member, Dr Ian G. Macdonald. This book almost passed me by, but when I saw it was scheduled for publication in May 2018 I advanced ordered it. It is written from a UK perspective, in contrast to Evidence Explained, and I consider it is a worthy book for any genealogists to have in their reference library, along side, Evidence Explained.
- There is also a useful page within the Family Search Wiki
- Recording of a presentation, given by Diane Elder at RootsTech 2018 – the title of which was Source Citations – the Good, the Bad and the Ugly.
- Hints & Tips 5 – Genealogy Standards & Good Practice by the Society of Genealogists (London, England)
Disclaimer – I have not financially benefited from naming nor recommending these books. I purchased the books myself and all comments and opinions are my own.