I would expect this feedback to be coupled with specific suggestions for how to achieve it.
While I'm sure there is general advice for how to do this, I think it would be best to ask your manager/teammates what structured and clear looks like, or specific examples of your previous unstructured and unclear communications.
To me, structured and clear means written down, broken into logical sections that build upon previous sections without scattering whole pieces of information.
For me, this has meant repeating information, even if it would be better to define something once and refer to the definition later (like a pointer) -- but documentation is not software. Hope this helps.