Step 1. Find someone else.
Step 2. Find an empty room with a green screen.
Step 3. Bring the other person there.
Step 4. Position other person in front of green screen.
Step 5. Start the video camera.
Step 6. Have sex with the other person.
Step 7. At what seems to you to be an appropriate ending point, stop having sex.
Step 8. Stop the video camera.
Step 9. Stand around awkwardly until the other person gets the point and leaves.
Step 10. Lock door behind the other person.
Step 11. Digitally overlay sex footage with a green-screened background of furniture, lots and lots of glorious furniture.
Step 12. Imagine that you actually just had sex with the furniture instead of the other person.
Step 13. Ahhhhh yeaaaaahhh...
(NB: Also works with real furniture provided you don't bother with the other person, although it requires considerably more romancin' on your part.)