i hold a cord end with a clothes peg near a flame,
then pull the cord through the clothes peg hole,
including pausing for 3 seconds (3mm polyester cord) with the melted end just inside the level of the clothes peg face,
then yanking it out.
this has evolved to just pulling the melted end through the peg,
and then again with the cord rolled 90 deg.,
which smooths the sides that have been pinched a bit by the clothes peg profile.
in the same way as knotme discussed,
i join ends with lighter or candle, and just put the two ends together,
then have had success with neatening the join using pliers
pic:
my clothes peg (reva australia),
3mm v.b cord finished end,
joined ends shaped by pliers,
and my igkt scale / colour card !