Make a slip knot (start of a chain) with a short tail.
Insert the new thread (green) through the loop.
Pull both ends of the slipknot.
You are successful if you feel a slight snap. To test, pull on the green thread. If it pulls apart, try again.
If done right, this knot will not pull apart like a square knot will, and the added bonus is that it is smaller.
Other instructions seemed complicated to me, and I couldn't remember it the next time I needed to tie a weaver's knot. I needed something I could remember without having to get out a book. What could be easier than remembering to start with a slip knot?