I just attended a knitting class last week on Blocking at my local knitting store. I have tried damp cloth blocking and spray bottle blocking before with poor results so when this class was advertised as "it will change your mind about blocking," I felt challenged and very skeptical!
It was, by far, the best knitting class I have ever attended!
We learned to block using the steam method. We blocked a piece of knitting using 3" T-pins on a large piece of foam (bigger than a couch cushion) covered by gingham fabric. Using the steam from your iron, you "hovercraft" (literally holding the bottom of your iron's steam holes fractions of an inch above the knitted work) over the outer edges of your garment first, before moving to the middle of your garment, and steaming it. The idea is that the steam will "soak" your yarn, but the heat of the steam dries quickly. You let the garment dry and cool before you steam block it for a second and last time.
It was beautiful watching the yarn relax under the steam, and although it was a little nerve-wrecking to practice this method in front of others in the class on someone else's beautiful work (!!), it was amazing to see the results before me.
After trying unsuccessfully to block in the past, I am now convinced to use this method in the future (starting this week!) Apparently it will work on a scarf knit in st st, although the very nature of st st to curl will probably reoccur after washing it.
Hope this helps, and if I have been unclear in any way, please feel welcome to ask me more details.