Self and peer assessment can be powerful — pupils think hardest about success criteria when they apply them to work — but they fail badly when the criteria are vague, the expectations are not modelled, or the activity is treated as a marking shortcut for the teacher.
Make success criteria concrete and visible. 'A clear topic sentence' is too vague; 'A topic sentence that states the writer's argument and previews two reasons' is usable. Pupils need this level of specificity to give meaningful feedback to themselves or each other.
