"The site is slow, can you fix it?" is probably the message I get most.

Before touching a single setting, I look at four things:

1) how many plugins are active, and which ones load on every page 2) image sizes (a 4 MB hero photo is still the most common culprit I see) 3) whether any caching is set up at all 4) the hosting plan, because sometimes the honest answer is that the server is the problem

Most of the time the fix is boring: remove, compress, cache. No magic plugin needed.

What's the first thing you check when a site feels slow?