Bear in mind that each subject of your essay has to have the same kind of characteristics evaluated.
In case of previously mentioned artists, both of them should be covered by analogy: if you refer to educational background of Artist 1, you have to mention Artist 2 educational background as well; if you omit information about Artist 1 early works and concentrate only on his most famous period, you should not get into early painting years of Artist 2 either.
In such a way, a topic that would otherwise be too general is narrowed down to a specific aspect that you will study.
When you’re comparing artists and their works, your task might be to concentrate on similarities in their techniques only, as opposed to genre and other attributes of art.
In a subject-by-subject comparison essay, the thesis statement should be located in the introduction, as usually.
Then, enumerate all the relevant features of the first subject and proceed to the next one.
To compare generally means to measure similarities or dissimilarities between things.
However, when we define comparison for compare and contrast essays, the definition is narrowed down to the "similarities", while contrast comes in to take charge of the "dissimilarities". The task of a compare and contrast essay is to discover the nature of possible connection between two or more subjects.
Putting your understanding of these things into writing, you learn the art of argumentation and expression of reality through your frame of perception.
Moreover, you attempt to discern relevant ideas out of a variety of those less important.