First, you must press your leaves. It's a lot like pressing flowers.

1. Put each leaf between a couple of paper towels.
2. Layer the leaves (and paper towels) between 20 pieces of paper. An old phone book works great.
3. Place a few heavy books on the entire stack to help flatten every thing.
4. Your leaves should be pressed and dried in about a week.

To preserve your leaves longer, place a leaf between two sheets of wax paper. Put a cloth on top and iron. This will transfer the wax onto the leaf protecting it longer.

For more leaf ideas try:

Look What I Did With a Leaf!
by Morteza E. Sohi