I usually find a bunch around brick or cement walls containing openings/crevices. They like to build webs at the bottom of the walls and hide in the crevices when disturbed. I can see them while taking walks at night, but you'll need a flashlight as their bodies are difficult to see in low lighting. After I spot the webbing, chances are there's one.
i've found it is generally easier to find widows in civilization or on the border with wild areas. all the webs i have seen have been pretty low to the ground
as laoticus pointed out, widows almost always have a retreat or hole or crack they build their web around that lets them run away and hide from any disturbances. the main trick, once you find the webs that have widows in them, is to keep the spider you want to catch from making it to it's hiding spot
don't really bother looking during full daylight. you can find them, but only a tiny fraction of the widows come out during the day
start getting used to how strong various webs are. some webs are so weak you can almost not feel them when you break them. widow webs are probably the strongest in the united states. not only can you feel them but you can actually hear them as they break. they make a sort of crackling sound
Did you not read my replies to your last thread on this subject? Those slings are probably about ready to hatch slings of their own by now.
Black widows rule the community garden where I have a plot to the point that we're about ready to put up signs that say "Careful - Deadly Spiders Crossing."
p.s. It's true that they don't come out in the daytime, but finding them is as easy as falling off a log. The telltale web - a gossamer mess - is visible everywhere - you can't walk between plots without getting entangled in one (and a Black Widow web is NO JOKE, let me tell you!) And my plot is situated under a street light on Fountain Avenue - so when I go to visit the garden at night, it's illuminated by a ghosly glow, and the Black Widow brigade is out in full force.