We’ve seen it happen in several client accounts so you may want to try this for yourself.
One, if you’ve got a great performing campaign…consider revising the landing page with a new look and streamlined content for better performance.
Two, a great way to bump a good performing campaign to the next level is to update your ad text. Introduce a set of new ads. For some reason a fresh look, or fresh approach can also push your ad click through results. Buyers sometime experience ad fatigue and so a fresh approach periodically can reap really big click and click through results for an already great performing account.
Third, try break out ad groups. When we have a top account another way to push it to even better performance is to break out the top performing keywords into their own ad group with their own landing page. This very narrow focus and match on ad text, keywords, and landing page is a winning combination!