This is the easiest part of the process. When your website has reached its peak and is No 1 or lower, it does not matter as long as it is above the fold. You will obliviously want to make sure it stays there and the best way to do that is to add a new page related to the niche once a month and create a new article on an external website with the author bio linking back into the website. This will help keep Google interested in keeping your ranking. If the competition becomes very high, make sure you backlink as much as possible to stay ahead of the competition.
A lot of the time they will be competing like you are and trying to get the higher spot. If they realize they have very little chance because of all the backlinks you have, they may back off and not try to compete. In the same way, you would if you saw a high dose of backlinks for a competing site.
In closing, I hope this guide has helped put you on the right path towards your goal in succeeding with Adsense. The more sites you make, the better. Obviously, not every single site will be super successful but as you gain experience in creating Adsense sites, the sky is your limit.
All the best!