The relation between Structuralism and poststructuralism is a relation of extension , critique and antithesis. From De Saussure's structuralist thought to Derrida's deconstruction-based poststructuralist philosophy, it is a linguistic vision that thinks the relation between the Signifier and the Signified, simplistically put, the relation between the word and the world. While Saussure does talk about 'pure difference' between signifiers in a language and also the arbitrariness of the sign, he nevertheless, thinks that there is a structure (order, unchaotic) in language which comes from the general system of Lang and plays its role in controlling the arbitrary problematic of the parole.
In the poststructuralist ambit, it is this 'pure difference' that is absolutized by Derrida who thinks that the Signifieds unreachable and similarity is not the operative process of language. He, in turn talks about a 'free play' of signifiers which proliferate endlessly. The 'transcendental signified' is an absence and the signifiers keep differing and deferring in a quest to reach their Signified, never to be. This is how the centre is dislodged from the structure as it is seen to be located both within and without. This decentring and a radical Differance of meaning clarify the point of contrast between Structuralism and Poststructuralism.
For a literature review, structuralism asks that you read and critique the work looking to see if the author is simply applying a "formula" to create their story - copying basic conflicts and plot lines from classic texts - or is the author creating something original. It's like appreciating a really good new song because even though the notes available are finite, the style, structure and voice of the song can be thoroughly original. A structuralist will be quick to point out where a text fits into predetermined categories or styles and what the similarities are to other works.
Post-structuralism asks you to have a more opened mind and to realize the originality is in your experience with the text. Even if it is a formula story, it is not plagarism and should not be dismissed as a copy or critiqued as one either. Where does the story take you? What is your reaction? If it brings you a unique experience than that is all you need to consider. Post-structuralists hate labels and boxes and categories for creative experiences. Both you and the author have had a unique experience in the text and that is where your reading and critique should center.