I would suggest imagining this scene in real world. What would the differences be?
-usually windows don't cast such bright, warm-colored light, unless it's a studio with some halogens there, or unless it's very early morning/evening with some very specific lighting conditions - I would use Corona's Sun+Sky setup with a more natural hue
-the dark areas are very dark, the bright areas are very bright - reducing contrast could help (either with tone mapping settings, or by altering materials)
-the contrasty yellow lights - this is just plain crazy, no one would want to use such lights ;)
-the flowers: it looks like you are using 100% red for the petals, and 100% green for the leaves - would be great to reduce saturation, and add some variation, also some reflectivity would be good
-detailed textures, high-quality models - even with great lighting your scene won't look realistic if the models and textures are very "CG-ish"
-take a look at some reference photos and try to reproduce the lighting, materials, and exposure