I needed practice! Or, I just wanted to have fun with it. :) This is Arwen's coronation banner in The Return of the King. Sorry for the picture qualtiy-- the material I used catches the light!
I made this banner out of a scrap from my Arwen costume I had way back in... fourth or fifth grade. The scraps were funny shapes, and it was hard to find one big enough. (Of course, when I was done with this, I found a giant scrap... the way things work...) I think this is simply lining material.
As you can see, I did not cut it properly. If you are going to attempt this banner, please do not do the same mistakes I did. Make sure you cut out the shape symetrically and make sure that your pictures align.
First, cut out the fabric. Then, hem the edges. I did not want to get out the sewing machine so I used felt glue-- and it is holding securely. Next, sketch the design onto the banner. If you use a gray Crayola marker on the lining material, it will disapear after a few hours. So messups are okay. :)
Now comes the fun part! Get out a couple of paintbrushes and a whole lot of white acrylic paint. Because you are painting on fabric, you can't water down the pain a whole lot, so be prepared to spend at least an hour painting.
Next, sew or glue the thingies on the top. Do those thingies that hold the banner to its pole have a name? Oh, well. Thread a dowel (or a stick that your brother sanded for your other brother to use as a wand... as the case may be) through the "thingies", and voila! You have a hanging banner! If you want to hold it like Arwen did, you will need another stick.
Here are the only two screenshots I could find of the coronation scene and banner. I used the Lord of the Rings Costume Research site's diagrams for the design (I found it interesting that the White Tree of Gondor is an Elvish design on the banner, not the typical design found in Gondor!).
EDIT:
You can see this banner in action in my Masquerade Costume post.
Second Edit:
Here are some candid shots of my brother, in his Aragorn costume, with the banner.