I was shown how to do this many years ago, (about 25 years ago if you must know) now I don't remember who came up with this but it was taken from a book. Now to do it properly you need a ruler but I've done this free-hand and with an injured hand.
So to start you need to make a square diamond 4 dots by 4 dots like below.
From the mid line go one dot backwards and do a second square.
Now join the dots to draw the lines like below,
Add the rest of the lines to complete the outline,
Then just add the finishing lines so the knot goes over and under itself.
You can add extra squares so your knot is longer, goes around corners or makes a border to go around your page. It can also be used to create a knotwork cross or, well just play around and see where it goes.
So there you go, a simple way to do a simple knot, or create images far more complex with knotwork.
