Cross-view images are, for most folks, the easiest to "free-view." The technique requires that you cross your eyes and try to see the left image with your right eye and the right image with your left eye. Your lines of sight are crossed. You will see two sets of images and the goal is to get the two sets to "merge" or "fuse" in the center such that the sets overlap. Where they merge, a 3D image will appear. Learn How Here
It can help to hold the tip of your finger about 6 inches (15 cm) away and look at it while paying attention to what is happening to the images on the screen. The screen images will become two sets of images and they will seem to slide apart and together as you move your finger away from, or closer to your nose. At some point they will "merge" or "fuse" into a 3D image.