I need help with the wallpaper I'm doing now.
It looks half done, and not very promising either...
Some comments & suggestions, please.

Wallpaper here:
http://www.animepaper.net/gallery/wallpapers/sessions/item66573/

Right
i love the pose
very nice
there's a little bit of white around his leg, so you should remove that
make the scan stand out more
it looks like there's a semi-transparent purplish layer on top.
scan is a bit grainy, so if possible, fix it.
and now to the background
ITS ALMOST EMPTY~!!
See if you can add something that doesn't look out of place.
Make sure it doesn't look crowded either.
I find it really hard to add stuff onto the background,
so I wish you good luck!