I've been using a different knotting technique than this for the past few years to join a new skein of yarn, but my technique leaves a bulkier bump at the join. This weaver's knot technique, demonstrated by Yarnspirations, appears to leave a smoother finish at the join, so I'm saving their video here to help me remember how to do it!
However, try as I might, whenever I use the above method, I ALWAYS have one end that pulls out when I try to tighten the knot.
So, for me, the method below, demonstrated by theweavingloom3304, is the only way I've successfully managed to tie a weaver's knot.
And I have to say, this technique does result in a much less bulky join than the knotting method I've used in the past, so I need to practice it enough that I'll be able to do it correctly from memory!