@netmeg we already got two answers on this from John Mueller (though the answers are broad), the link is in another thread.
But yes, it's wise to act. Perhaps be careful about some of the suggestions you might read about. Just remember NONE of us here know anything other than our limited observations and speculation.
I've heard some 'experts' in the G. Product Forums give some spectacularly dangerous advice. Be careful!
I'm personally still following the formula of 'content is king' even though that's not necessarily 'in action' currently. I've also corrected a few 'basic' things, like de-indexing some profile pages, some of the navigation hub pages, and some tag pages. (On Mueller's / and a few of the better G.P.F folks advice)