Most of what is applied as layer number one will be covered by the middle and dark values. It's important to keep this in mind, since the painting often looks pretty wimpy when all there is are the pale, first layer shapes. Keep the faith. No need to make sure the viewers can tell what they're looking at yet. In fact, it may never be necessary. Forget the names of the entities your shapes and values refer to. Let the content take care of itself. If you have trouble letting go of the narrative, turn the image upside down.
Even after the mid-value shapes have been applied the work in progress can feel as if there is no substance, no light or space. Resist the temptation to bring individual areas into further resolution. Get the whole page to a similar degree of finish first, trusting that the darks will do the rest of the work.
About those darks...
They are usually not all the same color, and very rarely are they all black.
These urban alley pictures will respond very nicely to a simple three layer treatment. In fact, the darks alone could tell most of the story. Try working very quickly. You'll find that the process can unfold rapidly when you're not burdened with the need to describe the content.
You can also relax regarding edges. Let things run together, especially in the early stages. Concentrate on the values. We'll still know what the subject matter is.