Ask HN: How do you increase the performance / impact of an engineering team?

I'm an engineering manager at a growing startup and looking for advice on how other EM's increase the performance (measured in whatever way you measure it e.g. impact on company metrics, features shipped etc.)?

One of the common answers to this is 'depends on the issues you're currently facing', which is 100% the right approach, however I'd love to hear advice on how you identify these issue root causes. E.g. if the issue we are facing is that 'the performance of the engineering team has degraded over the last X months' - (not an actual issue just an example) how would you approach identifying and subsequently solving such a broad issue?