My 7.5 General Guidelines for Reviewing Journal Articles

I am involved in a few editorial boards and as part of these duties, I get the occasional question about what it means to be a reviewer and what is required if doing a review. There are some great resources on the web, look for example here, here, and here. These links have some excellent suggestions for evaluating the suitability and quality of a manuscript.
Hence, my goal is to just simply add a more personal view on reviewing and some guidelines.
Science in its current form rests on a peer review, the scientific research process relies on improving ideas, methods, designs and theories through discussion with peers. The review process is just one aspect of this.
So here are some rather random guidelines:

1. Be fair 

This may be the most important guideline. Research should be objective and dispassionate, but this is often hard to maintain. Researchers spent most of their time working on a project and become highly identified with their scientific 'babies'. It is easy to become opinionated about your and others research. The theoretical lenses through which we conduct our research will lead to biases and preferences. Do not let these professional blindspots guide your reviews. Evaluate the submitted manuscript on its merits and what you consider to be weaknesses. State your own biases or assumptions, if this helps to clarify why you argue a particular point. If you know the person (experienced researcher will easily identify the author of an article), do not be tempted to engage in personal feuds (e.g., "I will get back to you about that nasty comment you made at my last presentation in XYZ" ;). Stay professional and evaluate the manuscript on its scientific merit.

2. Be supportive

Help authors to find the parts in their manuscript that are less clear. Researchers are passionate about their research, acknowledge the strengths of the study. It often helps to quickly summarize what you consider to be the key points. This will show that you have understood the manuscript and also may highlight some additional points that the authors may not have thought about yet.

3. Be critical

Evaluate the whole manuscript in its style and content. What areas need improvement? Are there alternative interpretations of the data or the results? What are flaws or problems in the argument or theorizing that you can see? Where are ambiguities in style or expression?

4. Offer constructive suggestions

Help authors to improve their work. This is the reason why we have a peer-review process! Provide references to additional literature. Suggest theories or interpretations that help to shed light on the research.

5. Be open

Research is about charting unknown territory. There may be ideas or approaches that may appear strange or  unconventional. Don't judge ideas prematurely.

6. Consider the bigger picture

Research often tends to focus on very narrow aspects or specific questions. It can be helpful to consider the wider picture again, especially if there are implications for real world problems, people or communities. If you see some implications or applications, highlight them. I believe it is important to consider how research can contribute to society. As a reviewer, you can help authors in this respect.

7. Do it!

One of the most frustrating experiences as an editor is finding reviewers. We often spend hours on the internet and going through papers, journals or books in order to identify some suitable reviewer. To get declined review requests can be very frustrating. Of course, there are legitimate reasons to decline a review. You may not know much about this area (so my mistake of inviting you in the first place). Don't review if you are not qualified to comment on the research. You may have personal or ethical reasons for not reviewing certain papers. This is all fine. An editor can understand this and appreciates a quick email stating these reasons. But on the other hand, there are more and more pressures from universities and institutes to publish. Reviewing is sometimes seen as a waste of time and a nuisance by some academics. I know colleagues who proudly confess that they have never reviewed a paper. I think this is unacceptable. If we all behaved like this, the process would break down.
Get engaged. Help with shaping research. Get inspired with new ideas (after all, you are seeing research as it is unfolding in its final stages). Do it! We need you! 

7.5 .... and submit your review on time 

Have fun reviewing
:)