What should I do to prepare my house before the PNW rainy season?

Six items, mid-October: clean gutters and downspouts, check and extend downspout runouts, seal any exterior wood cracks with caulk, verify the sump pump works (if you have one), swap furnace filter, and test every smoke and CO detector. This routine takes half a day and prevents 90% of the wet-season damage we get called for.