Three types of sites and promotion goals. Mutual understanding with the customer. Plan of work to promote the old site. Registration in services (Yandex Webmaster, Yandex Metrica, Google Search console, Google Analytics). Detection and elimination of errors: malicious code, content of little use, re-optimization, imitation of user actions, manual actions, non-natural links. Developer console and errors. Convenience and adaptation for mobile devices.

https://www.seotools.ru/kursy/23-oldsite/