Nikon allows you to produce double exposures in camera!! Find this under Shooting Menu> Double Exposures. Just choose the number of exposures you want and check Auto Gain On. Then press OK and quickly shoot the two exposures.
That's the easy part. Remember to pre-visualize what you are shooting. Choose the background or surface texture shot carefully. Note where the different surfaces will overlap your image. Adjust as needed. Shoot the main subject first and then the background or surface texture shot. The main subject needs to have a simple background to work. Here are some recent examples taken during a workshop up in Maine on Nudes in the Landscape with Karin Rosenthal.
See what can be done without Photoshop! In Camera!