Avoid "should".
Bad: Scientific claims should be linked to a peer-reviewed source.
Good: We require that all scientific claims be linked to a peer-reviewed source.
Great: Link the text from each scientific claims to a peer-reviewed source supporting the claim.
Using "should" communicates that the researcher can revise if they want, but are not necessarily required to. When leaving a review comment related to a requirement either state the requirement they aren't satisfying explicitly or start the comment with an active verb communicating what needs to change for that section to be approvable.
Using "should" often fails to communicate why they need to revise a section. In the "Bad" example above, the comment fails to communicate why scientific claims should be linked to a peer-reviewed source. The language creates ambiguity around if this is the reviewers opinion or a platform requirement.
Avoid "I think".
Bad: You should state hypothesis in the abstract.
Good: We require that you state your hypothesis in the abstract.
Great: Clearly state your hypothesis in the abstract.
Using "I think" indicates that the comment is the reviewer's opinion. When leaving a comment relate to a platform requirement either state the requirement they aren't satisfying explicitly or start the comment with an active verb communicating what needs to change for the section to be approvable.
Avoid "please".
In most cases where you want to use "please" the "please" can be removed to make the sentence more concise.
Original: Please elaborate on how you will collect samples?