Is it necessary to perform ritual A to perform further ritual from the boook NAP?
Yes. It is intended to put you in the right mindset to perform the rest of the rituals in the book.
Other similar techniques on other types of magickal workings include, but are not limited to: relaxation rituals, different kinds of meditation, breathing techniques, and such.
In the case of NAP I suggest to always follow the instructions so you can get better results, especially if you are new to this.
with any book and any system, if you’re inexperienced with it do as the book says. Follow its cake recipe. Once you’re it more or less nailed down and have experience with other forms of magick or other system then you can start to “wing it”… Or not. Just my opinion of course.