Let's have 60% for example
If this is made into a fraction, we would have 60/100, all we have to do is to simplify this. If would become 6/10, and, when divided, we would get 0.6
That's the long process, or the explanation for the technique.
The technique is to simply move the decimal point 60(.) to the LEFT TWO TIMES. So, it would become >> (First) 6(.)0 >> (Second) 0(.)6