Here are some advices and links to such:

https://www.researchgate.net/post/Does_anyone_have_guidelines_for_how_to_do_a_peer_review_on_a_paper

Be genuine in what you do.

Dear Stylianos Mystakidis

Your review should be clear, constructive and consistent. Clarity is important because authors will not be able to respond to your concerns if they don't fully understand what they are. Reviews are most helpful if they don't just criticize, but also make constructive suggestions for how concerns may be resolved.

Best Regards

Dr. Fatemeh Khozaei

As per my personal opinion, you need to have sufficient analytical skills of pointing/writing critiques of each section of research paper, if there is any, including grammatical error also as well as providing constructive and applicable suggestions.

Regards,

Hi

i think we should have two perspectives in our mind while becoming a reviewer...one , we have to complete our assignment within time limit and that should be 20-25 days not months......second concerned expert should deal the concerned assignment so that we cannot sacrifice quality of the research paper....

Dear Rifat Bhat , Ajit Singh , Fatemeh Khozaei , Kolita Weerasekera , Wolfgang R. Dick , thank you for your quick and constructive advice so far, contributing to the larger community. Here is my own two cents: One valuable practice that has aided me significantly in academic peer reviewing is actively searching, reading and comparing the reviews of other researchers on the same manuscript I have reviewed. This usually can take place in the second or third round of peer review. This practice has helped me see what I missed, understand how other, more experienced colleagues think, examine and critique a paper.

Looking forward to more input and insights by more colleagues!

I very much agree with the above points especially Fatemeh Khozaei's points about being clear and constructive. It helps authors respond if you number your points. It's fine to look for mistakes and weaknesses. However, it is no less important to decide what the authors are doing right, why are they doing it the way they are, how rigorous is their approach and how important and robust are the resulting findings. Never use reviewer anonymity to attack or insult any author. Use your reviewer position to make the manuscript better for the academic community even if it may not be accepted for a given journal. Try to make positive suggestions that would improve the work that will not take large amounts of added time, effort, or expense. Do not tell the authors that the work should or should not be published. Leave this publication decision for the editors. As reviewer, you can recommend to the editors that the work would or would not be suitable for the journal and why, what its strengths and weaknesses are, and how it fits into what is known and with unanswered questions as appropriate.

Dear Prof. John Tainer thank you for the fine suggestions.

I agree with Prof Tainer's comments. I would add that reviewers' comments should be prioritized so that it is clear to the authors which issues convinced you, as a reviewer, to suggest your recommendation to the editor. For example, comments could be listed as major concerns or minor concerns. Sometimes reviewers try to justify rejection of a manuscript by listing a litany of every criticism imaginable.

I also agree with prof John Tainer‘s answer

For me, a strong argument to clarify the statement and the coherency are major factors in crafting an effective and innovative essay with the visibility of the individual contribution from the author's part.

Dear Prof. Michael T Fasullo thank you for the insightful suggestion to prioritize and differenciate between major and minor issues/concerns.

Dear Prof Kundan Aryal and Prof Vinod Kumar Goyal thank you for your participation in the discussion.