As far as an actionable thing goes, my N == 1 experience says that regular nasal rinsing reduces both frequency and severity of various common colds a lot.

I used to be down with sore throat, running nose and light to moderate cough some 5-6 times a year, since I was a kid until my early 40s. Once I started with the flushing, it all went away. Nowadays, about twice a year I "catch" something, which means a single night of chills and sweating, and in the morning I am fine again. The mucous membranes seem to be no longer susceptible. No sore throat ever etc.