Peer review assists the editor(s) in making editorial decisions and also assist the author in improving the paper.
Any selected reviewer who feels unqualified to review the manuscript should notify the editor and excuse himself from the review process.
All manuscripts received for review must be treated as confidential documents. They must not be shown to or discussed with others. Information or ideas obtained through peer review must be kept confidential. All peer reviewers are requested to disclose any potential conflict of interest and should state explicitly if they have no relevant conflicts of interest to disclose.
Reviews should be conducted objectively and should express views clearly with supporting arguments. Personal criticism of the author is inappropriate.
Reviewers should identify relevant published work that has not been cited by the authors. Any statement or observation, derivation, or argument that had been previously reported should be accompanied by the relevant citation. A reviewer should also call the editor’s attention to any substantial similarity or overlap between the manuscript under consideration and any other published paper of which they have personal knowledge.

Resource for the reviewers:

Please read  the COPE Ethical Guidelines for Peer Reviewers (link)

Pannell, D.J. (2006). How to review a journal article: requirements, tips and strategies, Discussion Paper, School of Agricultural and Resource Economics, University of Western Australia (How to review a journal article )

More information on conflict of interest WAME (link)