You need better materials (the bricks are tiled, the asphalt has no texture, etc.). Do a search for high-resolution free or paid textures on the Internet (bricks, stucco, asphalt, landscaping), import them into SU (I'm assuming that's what you're using), and apply them there before export to KT. There are also asphalt and stucco materials, for example, to download from the KT library. You can also download some free noise maps from the Internet to apply in the Bump Map channel of the Material Editor to break up the pattern of the asphalt. Best would be to learn to apply an asphalt image post-pro with Photoshop or Gimp.
I would change the angle of the model so that it features the building and not the street. Also model the curbs, sidewalks etc. for a more realistic effect. Model the buildings in the distance. Is the main building supposed to be sitting on some kind of paved surface? If not, then set it on a landscaped surface. You can also position trees outside of the image area to cast ground shadows to break up all the blank space of the foreground.
Use either one of the KT globals for the sky for a more realistic effect or apply a sky jpeg post-pro.