The stems can be rather tough. I use a sharp floral knife to cut the end to a sharp point for easy insertion into the florist foam. This also opens the bottom of the leaf a fresh opening to draw up water from the foam.
Insert the first Jade leaves parallel to the lip of the container, piercing the foam from the sides.
A slight upward angle will allow the Jade leave to droop over the edge of the urn gracefully.
You can follow the red lines for the first insertions of the greenery.