If you want to improve on your walling techniques, the best way is to do a background that is truly your own. By trial and error, only then can you get an actual feel of making a wallpaper and from that experience, improve on the overall quality of your future wallpapers. That is my recommendation.

Why? It is because using a real-life photo for a background doesn't need much of a second thought. Just pick a nice fitting background, put on an extracted character and you have a wallpaper. In some forums, this would be called a "slapped-on" wallpaper or instant wallpaper (just like instant noodles, add in hot water and it's ready to go).

Another thing is that there is nothing to comment about the wallpaper. The reason why there is a wallpaper section in anime forums is for people to learn how to make better wallpapers by receiving critiques and reviews. That is my opinion of wallpapers to its strictest sense.

Anyway, I'll still comment on the character itself (since that is the only thing commentable) and I think it's well extracted with some minor improvements still needed. Another thing is that the character is too blurred. If you want to go for a blurred look, my advice would be to create a duplicate layer of Lucy and then apply some gaussian blur (I always use either 2.5 or 5.0 for the value). Next, fade the gaussian blur by maybe 50% or so and then reduce opacity to your preference.

Anyhow, I do hope you can come up with a wallpaper which you can truly (and proudly) call your own. Who knows, maybe you will make a name for yourself among the walling community (and also anime wallpaper collectors) like Nat, Bantam, LSE, Sir Boingalot, Andrea, Red, Redxxii and many others.