For the leaves, look for a shape you like and be sure the back of the leaf has good texture. Some leaves are much more pronounced in their veining than others!
Once you have a leaf you are happy with, give it a quick spray on the front side with some adhesive.
Next, place the leave on the foam sanding block (or another kind of foam, just so it's something you can cut). Sandwich the leaf and foam between styrofoam plates and pressed firmly.