2 things: it's really fidgety to get an image positioned/resized/skewed exactly right on a flat surface and it's heavily dependent on how the picture was taken - if it's a photo. it's best done with a photo taken perpendicular to the surface, not at an angle up or down, normal lens (not zoomed, no barrel distortion, etc.). I've had to go back and take a better picture several times, or distort the pic back into shape.
Thing #2: if you use the same texture on more than one surface and change it/edit it, it will edit it on all the surfaces it's on. So I usually save a different version of the pic/texture if i'm going to use it more than once.