
First, cut the ribbon the same length as the diameter of your lamp shade leaving an inch overlap.
If there is a seam in your lamp shape make sure you start gluing there. Put a couple of strips of glue about 6 inches at a time to make handling the ribbon or trim easier.
Work your way around the shade and overlap the two ends.
Here is what the result looks like.
Here is a lamp I updated with another drum shade and no trim in my front room.