I start the year with instilling in my students that they MUST write in complete sentences. We also work on restating the question in the answer to strengthen those sentences. In my state third grade is the first year that students take the super important state test, and this strategy is crucial for success, so this is a big deal for us.
I teach my students the PQA strategy. They need to Put the Question in the Answer. This is one of the more simple acronyms for the same strategy. We talk about this within the first week of school and practice, practice, practice.