Here's what I did:
I found some "scarf-like" fabric...not sure what to call it, and cut it into a long strip about 6-8 inches wide. I think for the length I figured out how long I wanted the necklace to be and then I doubled it to account for the knots.
I then tied a knot in the bottom, forming kind of a tube but I never sewed it.
Then I started inserting marbles and tying knots.
When I got that the length I wanted, I took a piece of lace and sewed it to one side of the knotted necklace (you could glue them together if you wanted this to be a completely "no sew" project), then I tied a knot over that to cover up where I had sewn.
On the other side of the necklace I tied the two ends together and fanned it out. This gave the necklace an asymmetrical look which I think is fun. I also think it would be cute to put a flower or pin on that side.
The whole project would have taken me about 10 minutes had I done it all at once. I have done bracelets like this before as well.
Even my kids can make them! Happy crafting!