Let your child wander the house or backyard with a camera. Tell her to take pictures of angles: right angles, acute angles, and obtuse angles. Remind her of to look in places she might normally associate with angles. Tree branches are a great place find acute and obtuse angles, and corners of the house all make perfect right angles.
Print her photographs.
Have your child categorize each photo, making different piles for each type of angle.
Get her to glue the photographs onto a corner of the poster board. Try and keep the angles all together -- a lot more geometric figures are going to be added and you don't want the shapes to mix too much!
Repeat steps 1-4, this time taking photos of perpendicular and parallel lines. two-dimensional shapes like squares, rectangles, circles, ovals, and triangles.
If your child is feeling especially ambitious, allow her to take pictures of three-dimensional shapes like spheres, cones, cylinders, pyramids, and cubes.
Arrange all the shapes on the poster board, keeping each type of geometric shape in its own area. Encourage your child to overlap the pictures.. When the board is completely covered, she'll have an artsy piece of decoration featuring shapes from around her own house!