Previously, we also talked about this same Subway backdrop. And I was reminded of one more thing I learned that can make your backdrop shots look just a little bit better. First, study your backdrop image to see if it is similar to this one. The lighting in this subway backdrop does not seem to be one that would naturally enrich the color and saturation of the things under the light. Because of this, this first picture has an unnatural match of subject and background.
Now this second picture is after using the desaturation tool, and after the color saturation is taken down a little bit, it makes the subject blend more with the backdrop, and look more realistic. The change might seem subtle, bit it does make it look a lot more like a real location shot.
Here's another example (below). The first one is about what it might look like straight out of your camera (and the model has very tan skin with a lot of color). The second one is with that skin color taken down a little bit, again using the desaturation tool. You may notice that the second one just looks like a more natural match to the environment, and in the end, more realistic.