I have found that the best bet is experimentation. Some days they want it quick, some days slow.
In any case, here's how to learn to fish streamers:
1. Tie up a dozen clousers or whatever other streamers you like.
2. Leave all nymphs and dries in car. Take rod, heavy-ish tippet, lots of split shot, and clousers.
3. Pray to fish gods.
4. Fish streamers all day in different types of water and with different techniques. Really pay attention.
If the fly isn't getting down, add weight. Most of the time you want to feel the bottom. If you're hanging up all the time, take some off. There is a lot to be said for fishing streamers in shallow water, but most of the time you want to have that fly swimming in and around the rocks just like a normal minnow would.
Try fishing up and across, down and across, and straight up and down. Fish the streamers in the pockets, along the shelves and seams, and especially tight to the banks where there's lots of fishy cover. You can fish a tight line, you can dead drift, or you can cast upstream a bit and throw a big downstream mend and let the fly swing on on the loop.
If you're fishing a floating line, consider running straight tippet from line to fly. The heavy butt of a tapered leader won't knife through the water like straight 8 or 10 pound Trilene will. This time of year you can easily fish streamers with a floating line and 9' leader. I prefer fast sinktips for higher water situations, but they aren't necessary right now.
Jim McLennan has some excellent articles out there on streamer fishing - but nothing beats time spent on the water figuring it out for yourself.
And, by far most importantly, do not forget step 3.