I can not tell how many keywords you need to do, but when you taken most of them, there no reason your site ranking below them. Take your time and analyze which keyword is the easiest one to do, which is the final one need to do. The most difficult part for ranking is your back links resources, a high PR do follow back link could boost your ranking so much, but no one want to share how to create that kind of back links, I do not know neither. when you check the keywords back links on Google. you can get around 30+ easy back links for free.
Create a back link is boring part, but if you do not do that no one help you, unless you pay, but how can you control the quality? there are a lot of company do SEO service, they just say we can do ranking for you, and promise your ranking on the 1 st page, let me tell you one thing, there only top 5 can get traffic from search engine like Google. they even can not promise let keyword go top, in my opinion only the stable first one ranking can worth to pay that money, or you just buy the high quality back links one by one. Yahoo directory is an example, so many people say it worth, i never try but i am thinking why it worth, it could be high PR back link, but the most important is the traffic. Yahoo rank within 20 in the world! how can you guess how much traffic they can bring?
Do not hurry to buy the service, try to make clear first, then choose your strategy best fit you.
Edit by Yan http://uniwarehousewares.blog.com