I cut out the sky and placed it behind the subway layer.

I then erased parts of the subway layer to reveal the sky layer behind.

I cut out the watch face from the source image.

Then using the eyedropper tool I sampled colours from the underground sign (the red, blue and white)

I used a soft brush on a new layer over the parts I wanted coloured (see image for colour placement)

I then set the layer to overlay but this wasn't enough for the effect I wanted, so I duplicated the layer and set the new one to colour.

I then combined the layers by clicking on the top layer, then holding shift to select the botom layer and all inbetween.

then pressing ctrl-alt-shift-E (cmd-shift-optin-E on a mac)
I made a new layer that contained all of my selected layers as a copy, just incase I needed to go back and change anything at a later date.

I moved my "watch" layer into my subway layer and converted it into a smart object.

Then using free transform I resized the image and placed it over the underground sign.

I changed the opacity to about 50% so I could correctly place it. Then I changed it perspective to closely match that of the sign, before pressing enter (return on the mac) and setting the opacity back to 100%

I then cut out the emblem of the watch and used the same tecnique as with the watch face to colour it.

I then moved my emblem layer into my subway image, converted it into a smart object, resized it, moved it over to the wall and changed its perspective.

I then added a slight drop shadow as i wanted it to look like a small piece of artwork, like the ones that are scattered about in the underground.

I then used a levels adjustment layer.

Followed by a viberance layer.