A usable scope names deliverables and quantities: how many content briefs, how many pages of production, how many technical tickets, how many links, how many hours of senior time, and who does the implementation. "Ongoing optimisation" and "continuous improvement" are not deliverables; they are what a provider writes when they intend to decide later.
Two clauses matter more than the rest. Ownership: content, links, accounts and data must be yours during and after the engagement. And access: shared Search Console and analytics from day one, because a provider who reports on data you cannot verify is asking to be trusted rather than measured.