Multiple exposure works just like exposing a piece of film multiple times did in the old days. It is going to develop part of the image each time and unless you keep things in exactly the same place, it is going to look like they "ghost" in multiple places in the shot.

If you want to use multiple exposures that look like one thing, you need to make sure that neither the camera or subjects move at all.

If you are looking to do special effects stuff, you need to practice, plan the composition carefully and make sure that you have dark backgrounds in the areas that you want to expose later (or use a black mask to block out that part of the scene). Exposure is additive, which means that once light is exposed on a particular part of the image it stays there, this is why you need to be careful to put black where you want to do another exposure and have it not look very ghost like.

Another way you can have a little more control to simplify things is to take your multiple exposures as separate shots and then combine them in Photoshop after the fact by combining the layers using additive blending. This will let you align the shots to minimize the impact of camera movement or to place layers to overlap the way you want.