Dr. Denton outlined a few guidelines for reviewing papers properly.
Conflict of Interest - must be reported and lead to the rejection of the reviewing
A reviewer has always the option to decline the reviewing of a paper for undisclosed reasons
Importance of quality - Comments and suggestions made to the authors of a paper must be correct and sound
Don't get carried away - Rather than commenting on how something should be done, comment on how clearly or sound things are that were done
Summarize - the first few sentences of a review should summarize the paper, its approach, etc. to show the authors that the paper was read and to show the editor and authors that the paper was understood
Do not focus on grammar and spelling - You are not supposed to review the paper because of your English expertise, but because of your domain expertise
Corrections - When suggesting corrections, focus on formulae and figures