This was one of our few commercial assignments in second year. We had to shoot a toy car, and a real location separately. Then we had to put them together, and this is what came of my assignment.
I used the car from the image on the top left, the location from the centre left, and the sky from the bottom left (my result shown on right).
Considering that I came into this program knowing nothing about photoshop, I think I did a pretty decent job.