Here's an example by artist Ryuchi Yamashiro:
Assignment: Assembled Collage Featuring a Variety of Objects
Adding a variety of elements to a design creates interest, and prevents a design from becoming too stale or boring. There is a danger of appearing clutter, so restraint and a discerning aesthetic sense must be applied. The addition of a variety of versions of the same element can also create a sense of unity.
Go through magazines and find 20 different versions of the same item and cut them out. Assemble and paste these cut out items into a 8” x 8” composition. Be mindful of the elements and principles of design as you attempt to create a harmonious composition. Keep in mind the design as a whole, and not simply the inclusion of the required elements. Leave a 2" border around your design, mounted.
You should also consider the content of your work, implied by the item that you choose. Example: Apples = Fertility, eyes = lust, vanity. Creative solutions to this problem are encouraged.
Here's an example by artist Ryuchi Yamashiro:
He has varied his image by altering scale and proportion to create a harmonious design. Your elements need not be exactly identical, but should at least be of the same type of object.