The American Medical Association (AMA) Manual of Style: A Guide for Authors and Editors is an online, searchable guide on creating a manuscript. Topics covered include: authorship, terminology, quantitation, and preferred usage.
This style guide provides rules and examples for creating references for a wide variety of sources. It does not discuss creating superscript citations or writing style. The National Library of Medicine (NLM) created and maintains this guide. It is available free and no log in is required.