Ideally the head will go deep into the extension and then the right shoulder tags it after a retrace. The idea is the trade is entered very close to finding the right shoulder, such as using momentum confirmation.
On this chart the right shoulder is found using the curling back upward. Additionally the signal on the indicator finds a green trend bar.
It also is confirmed by the reversal.
The is constructed by finding a sharp movement in the opposite direction of the trend. To find the center point of the you using andrew's rules you typically pick a major swing reversal.
I often will instead use to find a slope that fits the overall trend and make the center line parallel to that rather than having the slope be very dependent on a single trade on the chart. However in this case using the swing low worked for the setup.
This example is a tweak of the chart from "Tata Power: Nice Short-term Opportunity" by techtrail.
The price 1st pulls upward away from the bottom line but then fails to reach the median line. This invokes the hagopian rule and you expect price to go at least that far to the other side of the bottom line. This yields an area to look for the head.
If price goes to that area and reverses upward then you have a potential head that you can use to validate your final right shoulder candidate.