SEO our website

We have a website which needs SEO work. I am serious on this project, so please do not bid if you do not have real interest. Follows are the general description of our present website rankings, which will be discussed more detailed if I find any favorable bidder: This website has been maintained by ourselves for the past year and our rankings were favorable some time before that some important keywords can be top ten in google and yahoo. But for some reasons, which I can not figure out, it drops down dramatically recently, especially in google, some keywords cannot be searched now. But in yahoo, it is still good, with lots of keywords in the top. Maybe it is because too many keywords appearing in the contents, which were added particularly by us, but I am not sure. l Current situation: One important keyword is number 1 in yahoo search and others are also on the top. But most of keywords are not so pleasing in google, which we need more of your efforts. l Now we need keywords provided by us to be listed on top search engines, [login to view URL] and yahoo.com. We need them to be top 10. l We need the SEO to be conducted in the English environment, as our website ranking is in the Google English environment. l Please introduce your SEO history as well as your case studies so as to make sure you are well competent of this job. l We need the price quote and the way of the payment (instalment/others? / When to be considered to be the start to pay, please say clearly) as well as the duration of the project. If any questions, please feel free to contact me. Thanks.