Starting with the sketch model, I began by experimenting with camera position; particularly focal length
tried out the "counterzoom" technique to see what the image looked like with greater depth of field
Liked the counterzoom, so extended it a bit further
added first painting to see how it looks
Did an occlusion pass to see how the final image would look
Added label to painting (it actually does have the details, but you can't read it at 1080p resolution ^^;), as well as tweeking the lighting
Added Parquet floor texture (really taxed photoshop making it - lots of big layers ^^;)
The walls seemed a bit "dull", so I tried adding a slight bumpmap texture to give a little visual "noise"