What you need:
BURLAP: I use red burlap that is 6 inches wide and 15 feet long, this results in an approximately 3 foot long garland
TWINE: you can also use thick thread if you want the color of the twine/thread to be the same as the burlap
TAPE: or a large sewing needle

How you do it:
1. Cut a 4 foot piece of twine, you want to have some extra on each end so you can tie the garland together.
2. Wrap a small piece of tape around the end of the twine. This will act as the needle as I do not own a large sewing needle. If you are using a needle, thread it now.
3. Thread your twine through the end of the burlap and tie it in a knot, leaving several inches at the end.
4. Now you will start weaving the twine through the holes in the burlap. You will do a weave every 3 inches* or so. If the weave goes over the top, the next will go under, and the next over the top. That pattern will continue until you reach the end of the burlap. It should look like the pattern below.
*If you want wider, bigger ruffles you can do the weave every 6 inches or so.

5. As you go along, you want to push the burlap to the end of the twine that is tied in a knot so you have enough twine (or thread) to do the entire piece of burlap.

6. Continue the top/bottom weave pattern until you reach the end of the burlap, then determine how loose or tight as you would like the garland.
7. Then, tie the end off. Leave some extra twine at the end that can be used to hang it or attach it to another piece of garland.

That is it folks!
As I said before, my 15 foot piece of made me a 3 foot garland. For my 7 foot tree, I used 9, 3 foot garlands. I was able to find my burlap on amazon for a couple of bucks a roll (it does not seem to be on sale right now but shop around you may be able to find something even better).
I tied all of my garland pieces together to make one giant garland for our tree.

Note on mine you can see the twine, but I love that, if you don't like that look you can use red twine or thick red thread (or whatever color garland you make).
Happy crafting & happy holidays!