Uniform Requirements for Manuscripts Submitted to Biomedical Journals  issued by the International Committee of Medical Journal Editors (ICMJE) includes standards for determining authorship and contributorship on publications.

“Authorship credit should be based on 1) substantial contributions to conception and design, acquisition of data, or analysis and interpretation of data; 2) drafting the article or revising it critically for important intellectual content; and 3) final approval of the version to be published. Authors should meet conditions 1, 2, and 3.”

Not sure about the authorship order of a work? Check out Authorder. Authorder® is a free, easy-to-use tool to allocate authorship order on publications.