The only benefit to starting with Rule 3 in this example is that it makes it slightly easier to draw the chain. This is because both N and J must precede G but are also preceded by variables themselves. As there is no specified order for N/J, they must be stacked on top of one another. Starting with Rule 3 just saves us from having to go back and edit our diagram as the stacked variables are central to the placement of the remaining variables.
Setting up our diagram would work just as well had we worked sequentially through the rules. Once you get more practice with sequencing games, you'll start to develop your own system for going through and diagramming the rules.
Hope this is helpful! Please let us know if you have any further questions.