A simple rhyme is sometimes used as an aid in remembering how to tie a correct Square Knot: "right over left; left over right, makes a knot both tidy and tight."
The Square Knot is also commonly mistaken for a Reef Knot, which uses a Slip Knot rather than an Overhand Knot as the final part of the knot.
A Square Knot should never be used to join two different ropes, due to the knot's tendency to slip or come undone. A Bowline should be used instead.
Public domain image, edited by Bob Lemen.