In 38 years of flying the only rule of thumb I have managed to learn and use is 3 times the height and around 10 miles to slow down from 250 kts.
Other than that, I think that unless you have a 8GB memory stick in your head, you will one day use one of these rules and forget whether it's times 2 or times 4 and is it the square or the square root?
Just learn to fly the aircraft and forget all these so called 'rules'.