Welcome toytank, from what I've read, presentation is a factor but I think the priority is to figure out where the fish are. By that I don't mean hot spots, but just where coho salmon are likely to rest in a river. There aren't really "hot spots", since migratory spawning salmon are constantly moving when opportunities arise. The fishing maybe fantastic at one location on one day, but it is common to find that no fish in sight on the following day.
Unlike chum and chinook salmon, which basically dominate all the main channels once they enter a system, coho salmon tend to look for heavily covered, slow water. Log jams, overhanging shaded trees, underwater logs, weeds, riffled water are some of the environmental cues that you should be looking for. Look for section of the river where current is very slow, or does not exist. In the Maple Ridge area, you may want to travel east, get a mapbook and explore several systems between your starting point and Harrison River. In fact, you are in luck as rivers in this section usually experience excellent coho salmon fishing in November.
Secondly, timing is important. Unlike other species, coho salmon are shy and usually tightlipped during the day. Best fishing, especially in low water condition, takes place during the first two hours in the morning. Heavy rainfall like what we are expecting tonight causes increase of water height and triggers mass fish movement. The river mouths are tidal influenced. Incoming tide brings fresh fish into the river. Outgoing tide can sometimes push fish downstream.
If you are flyfishing or spinning, choose slow or frog water as mentioned above. Coho salmon will follow the presentation as you retrieve/strip it in.
Good luck.