Having a "First Five Minutes" poster gives students a sense of direction when they walk into the classroom. Although it will take a few weeks and lots of reminding to get students into the routine, giving them a task and a sense of responsibility when they walk into the room can redirect their behavior, especially after lunch or recess.
Squares are so cool ... they get into every club! I explain to my students that squares are in the parallelogram club, the rhombus club and the rectangle club. This really helps the kids understand some complicated geometric nomenclature.