I totally agree with jens recommendations
Some simple things from my side too:
1. Your scene geometry is too perfect. That removes realism, try adding some noise modifiers, bevel your edges, "destroy" a bit your scene. Now everything is "boxy"
2. Your materials are also extremely flat. It seems like you have only used diffuse maps but not bump neither specular ones.
3. Your grass also ^. You could create some "real grass" by using patches of simple instanced grass. You cover your garden with instances and then randomize their size. IIRC there is an amazing arch grass example somewhere around in the forum.
4. As jens suggested use hdri lighting together with sun. Also create interior lights and the street ones. Put them in different light groups so as to control their gain inside lux. This way you can get day/night shots with one render or mix them all together for evening shots.
5. The leaves on your trees are all transparent. You have to use a transparency mask
6. Use more dramatic camera angles, as well as DOF. <-- That helps more than you may think
7. Use luxrender or post-production effects, like camera response filters, bloom etc.
I guess thats all for now, looking forward for your next results. Good start btw