Step 1: Collect Leaves: Go on a nature hike and collect some leaves with interesting shapes. (They do not have to have fall colors, like these do.)
Step 2: Make Crayon Rubbings: Place the leaves under a sheet of thin paper in an interesting arrangement. Regular copypaper works fine. Using the side, rub a crayon across the areas where the leaves are. This will leave an imprint of the vein patterns.
You can do this crayon part in green or fall colors.
Step 3: Paint Over with Watercolor: Using watercolor paints, paint over the crayon leaf patterns. This is called crayon resist because the paint resists or doesn't soak into the paper where the crayon is, allowing the crayon to show through the paint. Use a different color from your crayon color. This is where you can add your fall colors, if you wish, but they can also be done in shades of green.