“Don't trust a mirror that only tells you how wonderful you look.” -- Matshona Dhliwayo
"Pats on the head," effusions of delight and the like are not criticism. They dodge the issue of criticism, except in the case where the text being critiqued is so excellent, so far removed from improvement that there is nothing left to do but to express wonderment and pleasure. (This is a rare situation.)
Criticism minimally expresses to an author,"There are standards which are relevant here that your paper does not meet." To be constructive, the critic must go beyond, indeed, avoid simple formulations like,
"This is poorly written," or "This makes no sense."It is more useful - not to mention, non-threatening - to avoid using such statements entirely. One might say, "The problems with this paper are that ...." This foregoes unnecessary emotional engagement and does the work that a critique should do: specify what it is that makes the paper fall below expectable standards!
We may - and sometimes do - encounter the following situation: a disagreement as to what standards are applicable in judging a paper. For example, what is acceptable as a report in a business might be criticized in an academic context as a hodgepodge pasting together of plagiarized material. Understanding the context of presentation and the audience that will receive your text is, consequently, important here.
The best procedure as as constructive critic is to adapt the attitude of a team-member trying to improve the workmanship of a colleague. Don't hold back from expressing concern if you think there is a problem; but don't try to intimidate or "one-up" the person whose paper you are criticizing by delivering judgment, but withholding the reasons for it.
(Note that this essay itself is a kind of critique. Do you think it, itself, meets the standards it articulates for constructive criticism?)
For specialized applications of constructive criticism, see:
What is a Synopsis? Controversy Analysis Worksheet (Interrogatory)Cordially, EGR
Worksheet with Examples
Solving School Problems: a conflict resolution approach