Step 1: Materials
I had Shapeways print my model, which can be ordered here: http://www.shapeways.com/model/983341/nautical-themed-rope-coaster.html
I ordered the alumide material, but any of them will do.
2. A cardboard box
We'll be temporarily attaching the model to the box to hold it still while we tie the knot.
The pins both hold the model in place as well as serve as something to keep the rope in place with once we start tying the knot.
I'll be using 1/8" cotton rope while I walk through it. It's a bit thick for this particular model, but it's great for knot tying in general! I ordered it from Knot and Rope Supply: http://knotandrope.com/store/pc/1-8-X-1-200-3-Strand-Cotton-6p1936.htm
Feel free to use whatever material you have, though you probably want to stay at or under 1/8" for this model. I think smaller material looks better as you can tie more passes. The red coaster shown above is tied with lacrosse crosslace and comes in many different colors: http://www.lax.com/lacrosse-equipment/Lax.com-Crosslace-Spool-Lacrosse-String-Supplies-4157.html