We went out on a walk and collected a bunch of pretty leaves. Then we ironed the leaves between pieces of wax paper (iron on high, no steam--make sure to cover the wax paper with cloth on both sides!). Once the leaves were nice, flat, and dry, we were ready to use them.
I laid out a nice sheet of clear contact paper, sticky side up, and taped the edges down with painters' tape. We laid the leaves out on it.