Here are two worksheets you can use to teach the properties of polygons.
Worksheet 1 is about classifying polygons. The instruction to sort the polygons into some categories is meant to make the activity open-ended. The basis for classifying will be up to the students. This will encourage the students to sort the shapes in as many ways they can. Examples: convex vs non-convex, according to the number of sides, according sum of interior angles, according to whether or not they have parallel sides, etc.
Worksheets 2 is about dissecting polygons into non-overlapping triangles. You can use this to teach the sum of interior angles of polygons. The activity can be extended to dissecting the triangles in two right triangles. This is one way to explain to students why much of Trigonometry is about right triangles.
Download worksheets: Polygons