[For the most recent piece]
That is a good attempt, however she isn't blending too well into the background (which is a good start to a nice background - good job). I'd suggest putting a fractal or similar to this:
over her
lower body on lighten/screen - whatever looks good and stays subtle. This way, it won't look so much like she is just pasted onto a background.
Another way is to duplicate her, place the duplicated layer underneath the original, smudge it a little bit (so the smudge is visible around the sides of the focal) then play around with the layer settings. Some tutorials suggest this a lot, although personally I don't like the outcome (but you'll never know until you try).
Also, I'd suggest lightly blurring the outside of her. You've decided to cut her out of the background (which works for some people) however her hair etc looks a bit unnatural now. A soft touch up with the blur tool should do the trick.