As for Keywords, my advice here as a starting point is to have a great item.
You should choose a very good product because of market research, create a fantastic listing and have a very deep keyword search. Here, you should put 5 to 10 high volume, high relevancy keywords from which our tool will grow because we will start mining from the Auto Campaign, the Broad and Phrase match, the custom search terms users/buyers use to buy the product, and we’ll add them back to the system. Thus growing the amount of keywords you have and the visibility of your campaign.
Now, start with 5 to 10 high volume, high relevancy keywords. If you observe that the PGN is not evolving fast enough, you can always add more. For example in this presentation, I’m going to put test KW 1, test KW 2, test KW 3, and test KW 4.