The suggestions can be placed in a box, and are kept anonymous, so this enables students who feel shy about asking for a repetition of something will not be embarrassed by asking again. It also shows the students that their ideas are welcome and they can feel excited when their idea is chosen.
For adult ESL students, a "grammar review suggestion box" in particular, could work really successfully. Instead of them having to ask for a grammar rule, this private request will enable the students to receive an answer about even the most basic grammar structure, without feeling self conscious. And all review is good for everyone anyway.
The teacher can ask for one idea only at any given collection of ideas so that every one can be organized and taught by the teacher, making each student feel special and included in the activities of the class.
When all ideas have been used up, the teacher can request new ideas and collect a new batch of suggestions.