I love fishing streamers, and in fact will often keep fishing a streamer even if fish are rising to dry flies. I just have more confidence in catching bigger fish on streamers. Also, I am a smallmouth bass angler at heart, and I like throwing "meat".
But one thing...you gotta believe. There are plenty of days when you're only going to catch a few fish on streamers, though they might be big ones.
The quartering downstream cast is the easiest way of fishing streamers, especially if the fish are really on them. I like to have my streamer pointed at least partially upstream. The quartering downstream cast means the streamer usually swings out and down but with any strip or twitch it darts more or less upstream. This is a natural swimming motion for baitfish and many other aquatic organisms. Other than that, just keep varying your streamer movements until something happens. In moving water, let the current swing the streamer out, trying it with no strips or twitches, just a smooth outward swing away from the bank. Then try letting it swing out but adding some very short, gentle twitches, not strips, just keeping the same amount of line out and twitching the rod tip. Then harder, longer twitches. Then short strips. Then longer strips. Vary the cadence as well. Sooner or later a fish will take it and then you have a good starting point for what's working that day.
Also, don't be afraid to dead drift streamers. I like to dead drift through a deep run, with a few twitches at the end of the drift when the streamer starts to swing or rise off the bottom. Or dead drift except adding just an occasional twitch or gentle lift of the rod during the drift.
A fish taking the streamer will manifest as a twitch, jerk, and or just some weight on the end of the line. You'll end up setting the hook into a snag or rock now and then, but if something feels funny or the line does something funny, set.