I planted some hybrid willows this spring (mid april).
The guy I got the cuttings from told me how to do it and I seriously thought he was messing with me, but he said this is how he did his and they're 20+ feet tall now and have been there 4 years:
We cut off the lowermost branches that were at least as big as your thumb. We then cut off all the branches that were coming off that main branch and cut them into 16"-20" long pieces, making sure to keep track of which end was the bottom so that end would eventually be put in the ground, and put them in a bucket of water. So from a 6' branch, you'd get about 5 'sticks'.
I had talked to our local DNR naturalist and he told me to wrap the sticks in a plastic bag & refrigerate them for a week, then put them in a bucket of water for a week & plant them after that. I told the guy I got them from this & he said you could do that, or you could just leave them in the bucket of water (about 4" of water in the bottom, and you NEED to keep an eye on it b/c they'll soak it up fairly fast), put the bucket on the north side of your house for a week or so and they'll start sprouting roots, then plant them. I had enough that I decided to do it both ways.
Well, both ways worked equally well, but since it's obviously a lot less hassle putting the bucket on the north side of the house, I'd recommend that method.
I've got 100% still alive and some of the branches are already above my head this year!! From what I started with, personally, I find these things nothing short of amazing!
Disclaimer: I planted these in my house yard and I am religious about watering the heck out of them. I've got a soaker hose on them and I'd say they get about 4 hours of soaking per week, but I haven't used any fertilizer on them. However, I would think that if you put them in a place that was fairly wet you shouldn't have any problem getting the same results.