Search Engine problems

Sup, everyone?

I joined cuz I have a bit of some trouble.

I write webpages for money, and I have a client that is somewhat disturbed that his site, which I built, finds itself number 16 or so on Yahoo! search... I've done everything I thought I needed to to get the number up... I've modified the META tags, I've put repetitious lines on the splash page for spiders to catch, but somehow, instead of going up, it's gone down in number (it was 14 last week).

So... Any suggestions? How do I bring the listing up to the top for search engines?

Thanks in advance!
~Josh

P.S. The site, in case anyone wants to see what I've done, is http://www.spherepaintball.com