As Coley said (go figure), it's about finding the right water, but when you do, swinging is very effective for coho. I still lament the loss of my honey hole on the Lower Satsop, where I used to do better than most of the gear guys swinging marabous through the flat. That spot was one in a million. But anyway... You'll have your best success on fresh fish that are just moving into shallow-mid-depth flats, and occasionally in riffles. You definitely want to start out the way you do for steelhead ( get the fly down to the fish), but during the swing, an erratic twitch or 20 doesn't seem to hurt. I get most takes either right as the swing starts or while stripping in on the hang-down.

Another presentation that can be good is to cast up and across, put a downstream mend in your line, and then strip it through a downstream swing. Sometimes, they crush that. Just keep in mind that coho like to chase things. Sometimes, the fastest, spookiest presentation you can muster is what they want (or at least what triggers a striking reflex in their gloriously tiny brains).