Determining authorship of research papers can be complicated: who gets included and in what order? Because academic papers are integral to promotions, grants and recognition, conflicts can be avoided by discussing these issues among the research collaborators as the project begins.
Consider these issues
Other than indicating who are the authors of a work, authors have other responsibilities (adapted from Michael Kalichman's material):
Write clearly and explain methodology, data analysis, and conclusions to the reader can understand and replicate findings.
Avoid mistakes wherever they could occur in the paper.
Provide citations that agree and disagree with the work.
Publishing negative results are just as important as positiive ones, to keep bias from the literature.
Disclose potential conflicts of interest, whether financial, intellectual, or religious.
List private or government sponsors in the paper.
Be aware who owns the copyright to your work (it's often the publisher) and whether you need permission to reproduce your own paper.
Alert appropriate university offices if findings could lead to a patent to avoid delays in publications prior to patent applications.