This is how I created this image for a CHristmas card I did for some close friends this past Christmas.
First I took the background shot that I could use to place my subjects in front of.
You may be asking why if I am already shooting in front of the Christmas tree with my subjects. Well it just makes it a whole lot easier with the cut outs and they dont have to be perfect as I wont need to be so percise....

The first challenge was finding something for them to sit on that would look some what believable in the final results. It wasnt perfect but it was close enough as we couldnt do a reshoot as we had to get this done right away so we could get the cards printed and sent out to family and friends.

Again this wasnt perfect. I wish I could have had the little boy (Jackson) with his right arm a little higher.

Final result! I had to resize them a bit to fit all of them in the image. But if I would have shot them in studio it would have abeen a little more tricky to get the perspectives right. Wouldnt have been hard just  more on my plate as I wasnt sure if I could pull it off and make it look believable. The whole thing was to be funny but people really thought they were doing this as they workout and are really a fit family....=)
So what I learned from this was to really not try and over think things to much. My first try at this was making it way to difficult and it didnt work out so we had to reshoot it. Glad I didnt give up as I really liked this shot and learned that you should always try the simple way first.