If you want to sustain it: careful hiring for fit and non-negativity, establish strong norms around collegiality, seek fun, celebrate small wins, and foster social support.
In addition to finding out local factors to assess, the ''big 4," in my opinion, are role overload, social support, job control, and supervisor behavior.
I haven't used it, but this tool seems pretty good: Health & Safety Executive Management Standards Indicator Tool.