Today I serendipitously came across a quote on another forum made several years ago by someone whose opinion I greatly respect regarding critiques, "The most serious error that most commenters make is expressing opinions based upon their own style or work". This really hit home. Who am I with no formal art training to give a meaningful critique.
"Critique" is a commonly misunderstood concept. It is NOT a process to tell someone what they did wrong. Done well, it serves to inform the maker about their piece as seen through different eyes. The commenter must first be able to observe from a neutral standpoint and analyze what they see without reference to outside objects. You have to be able to get "inside" the object, put it on and wear it so to speak, and then be able to verbalize what has been seen and felt. A weak reviewer will hide behind pedestrian aspects like torn grain, sanding or tool marks, or finish application. Once the piece has been analyzed, some valuation statements can be made of course, but those should be limited to the piece's internal elements and how they work or don't work together. Done this way, the maker will gain perspective and can even be made aware of aspects of their work that they did not consciously consider, and the crit will always be a positive, and hopefully educational, experience for the maker. Telling someone their sanding technique "sucks" will go nowhere, and the maker's ego will throw up a defensive barrier to further comments making what follows a waste of time for both parties. I see many struggle to make a cogent comment and retreat into vague value judgments. This can be nice for ego-building, but it won't help the maker and may actually retard their personal development.
In the final phase, several kinds of suggestions can be made.
First, if there is an issue that the commenter finds weak or inappropriate, a suggestion encompassing one or more alternative treatments can be expressed as suggestions for possible use in the future. This can deal with anything from technical fabrication weakness which detracts from the other aspects, to material selection, finish choices, etm., which can assist the maker in improving what they do. Pointing out an error, however, must be discussed with a detail on why the topic is viewed as an error and its effect on the rest of the piece.
Second, references to the work of others can be used to illustrate a point or concept by pointing to how elements have been handled by others. This kind of reference should be free of value judgments about the piece being reviewed, but rather encourages the maker to broaden their perspective and personal knowledge base which will help them analyze their own work in a more meaningful way. Reference to the commenter's own work illustrates a bias and narrowness of knowledge which results in devaluing the entire critique to a bunch of personal choice "do it my way so I'll like it more" opinions.
The primary guideline is to tell the maker what you see without making value judgments. Doing so will allow the maker to make their own judgments about their work in the context of what they were trying to do when they made the piece.