After editing the images in Camera Raw (chaining clarity etc.) I first did basic editing on the skin. I removed under eye circles, little spots, make the lipstick edges sharper and evened out the skin tone here and there.
The next step was to cut out the image from the black background which was easily done using the Quick Selection Tool.
Important here was to pay attention to the individual polkadots that tend to missed in the selection. I had to go back a couple of times because I always missed a little detail.
For the time being I saved my Selected Rosie the Reverter onto a transparent Image Layer.
Meanwhile I created a gradient background based on the colours of the original image with help of the Eyedropper tool.
Separately I cut out the speech bubble from the original poster and placed it on the yellow background.
The reason I did not do the speech bubble myself is that my research showed that it is quite tricky to get the right font as well as a speachbubble like this.
To finsh the image Icopy and pasted Rosie the Reverter onto the background.
The rest was filing work. For example selecting a particular area with an adjustment mask to change something about it like the saturation of the scarf.
I also added a layer mask onto the Rosie the Reverter layer and softened the edges between her and the background. However I quite liked having a bit of a line as I thought it looks more like the poster aesthetically speaking.