I look for an active area, (they have a tendency to re-use old tunnels). Then I take a dowel rod and poke a hole in a tunnel, (I try to put them at intersections/Y's for better odds). I cut the worms in half and put half in the hole and pinch the hole back shut. I then wait a few days to a week and then flatten out all the tunnels. Then repeat process. I get 4 worms per package by cutting them in half and I'm guessing I cover approximately 100-200 sqft (10' x 10' to 15' x 15' area) with 4, depends on how much activity there is. I also try to put a worm in the "leader" tunnel where they come out of the woods. I try to get them in early spring before they breed. Sometimes as early as March. Now that I got them under control, I would say I'm pretty much done fighting them by the end of May and might have to fight them come fall, but I haven't had any activity for several months now. It's a little expensive using the worms to start with because I went thru quite a bit of them, but now it's probably only 2 or 3 boxes early spring and maybe 2-3 in the fall. Not real sure since it's a continuous learning process. I haven't been spreading insecticides like I know I should, to make a better perimeter, but my method is working satisfactorily for me for now.
These are the worms I use, approx. $20 at most stores.