I tried to recreate a plastic bag after watching a tutorial but failed to achieve the desired look. The plastic bag is supposed to be floating and moving with the wind but instead, while playing the animation, the bag loses its form and kind of collapses even though self-collision is turned on. The physics of the object (plastic bag) is set to soft body and I added turbulent and wind to the scene.
Try using cloth instead of soft body. I think that gives you better behaviour and control.
Make sure you object is made out of quads and they have roughly the same sizes. Especially for bending animations it's crucial that quads are as undistorted as possible. Then maybe add a subd modifier before your simulation. Keep in mind that the subdivisions an object has the smaller the wrinkles of cloth animations will be so ideally you use a subd before the simulation to give it enough geometry to work with and add another one after the simulation to smoothen the result.