Decide which one is going to be a foreground image and which one will be a background image. Select (Command+A) the foreground image and use the Move Tool to move it over the background image.
Now, you can start erasing the areas in the foreground image. I generally do not rely on a magic wand tool or magnetic lasso tool to select areas I want to erase. You can if you have larger area(s) to erase or select but this particular image had a lot of fine details to work around. Instead of using selecting tools, I worked with different brush sizes of the erase tool.
Once you’ve erased the parts of foreground image; align the foreground image with the background to get the most natural angle or a place. If you are happy with your creation – merge layers and go ahead to color adjustment and sharpening.
See, it’s really simple! Of course, you could also edit/erase the foreground image separately on its own transparent background and then move it over the background image but that just asks for a few more steps. Advantage of doing it that way is that you can clearly see what has been erased and did you miss anything.