Keyword Optimization

[foke]

Hi...
I have been working hard trying to improve serps for my site. 4 weeks ago, I was on page 15 for keyword nature wallpapers, two weeks later, I made it to page 1 (10th position). Everything was going good, but suddenly, my serps start to fall. I don't even get any visits from that keyword. Now I am on page 6 on google.

So, what do you think I can do to improve my site for "nature wallpapers"?

Here is the site:
[Link Removed]

Thanks a lot!