Levitation and Flying effects
This is not a particularly difficult technique but it is rather labor intensive. While it may be done using other programs which use layers, I will be discussing the process in Photoshop terms (I used CS5). I would also recommend you do your first levitation image with a model, as it is an additional complication to try to get the positions right when it's just you!!
As Tamara mentioned in the previous tutorial, the single most important thing in creating a convincing composite is to have a very clear concept before you begin. This is critical in composites as you will likely be taking separate pictures of the various elements, and you must keep in mind lighting, pov, angle, etc. that will look "natural" when put together. You can use a timer, a remote trigger, whatever you're most comfortable with. For the sake of consistency, I also use a tripod for ALL the pieces.
Once you have your concept, assemble all your props. Start with what I'll call the "establishing" shot (or "set"), which will serve as the background for all the other elements. For the main figure (you), you will need some sort of stool on which to sit/stand/lie. To make sure you are in a convincing position, I recommend practicing in front of a mirror.
Things to keep in mind when shooting are details that will give the illusion of movement. In the example image, I did about 6 different shots for the final figure: the flowing skirt, one shot each for the legs, another for the arms, and one for the hair. The streaming ribbon was part of one of the images and added in for compositional balance. Then shoot all your other elements, separately. For this image, I tossed crumpled paper, tissues, and plastic bags into the air. Remember to keep the lighting consistent for everything.
Once you've shot and downloaded all the pieces, the real work begins. Open your establishing shot image and save it as your base layer. Then extract the subject from every shot using your preferred method (I used Topaz Remask 3), and paste it into a new layer in the base document. For the figure, choose the image which has the most elements that work, and then just select the pieces of the body to add to that main image. Mask out the existing "non-flying" limb, and past the new "flying limb" in a layer above it. Adjust its position to look natural. You may also have to mask out a portion of the new piece in order for it to blend more naturally. Once you have the figure assembled to your satisfaction, merge all the layers to create just the one layer for the subject. Erase any portions of the stool/chair/ladder/whatever you used to support yourself. The floating illusion is now complete.
Do the same thing for all the image elements, insert them, and then just move them around until the composition works for you.
Once everything is in place, it's time to add the final touch for reality: shadows. It is amazing how a shadow can turn a good illusion into a very convincing one. There are many ways of inserting shadows, including the drop shadow feature from the fx button below the layers. This works in some situations (and I recommend creating a new layer from it if you do use this technique), but I often just create a separate layer and paint it in, using a very soft brush at 3-5% opacity. I use a separate layer for each shadow. In placing the shadow, stay consistent with the direction of the light. Realize that not every element needs a shadow, as in the sample image.
And that's pretty much it. Final editing touches are up to you. For this image (which was shot for a "grunge" challenge) I added a grunge overlay.
It is possible to shoot a location separately, then do the rest of the process in studio. You would process everything the same way, except you would have to adjust for white balance and other inconsistencies between the location and the studio shots.
Have fun! Looking forward to seeing your experiments!