How to fix creaking stairs

The internal stairs in our Brisbane high-set home are terribly creaky. This house was built in 1970 and as you will see the construction of the stairs caused the stairs to later on in time creak and groan whenever anyone went up or down them.
I am using the skills acquired from when I was a joiner and I had the privilege of doing my apprenticeship in a joinery shop that specialised in stairs.
So what I am about to show you is an easy fix to existing stairs that creak.