How to determine best keywords for my site

[Togemon]

Did I mention I have never built a webpage before?? Well one of my friend has a new site to basically sell an item.We both are working collectively for it and I am trying to learn how to optimize everything before I load it onto the domain that we bought for it. Is there any tools out there that can go through our site content (I do have it loaded on a unused unrelated domain) and find what would be best to use for keywords?
Well, to find a good solution I've tried to use adwords suggestion tool where I put my site's url to get suggested keywords then after getting the suggested keywords then I ran the keywords on keyword discovery or wordtracker to get the estimated traffic. But all these couldn't help me the way I way I wanted it to be.
Can anyone tell where did I go wrong? Please solve my query or suggest the best possible to get rid out of this trauma.
My basic concern is how to determine best keywords for my site so that we have a good sell of our item.

[Eustorgio Leonardo]

Hai,
Once you develop your web site and optimize all pages for keywords you would like to know how many of those keywords get you visitors. Now, GoogleRankings.com provides just that. Its easy interface helps you quickly ascertain which keywords work for your web site. This is one of the coolest services for finding search engines rankings based on keywords.

[jasonbourne9839]

According to the website you can examine the keyword or you can use Google adword tool for searching more keywords.

[Amit Airon]

Google adwords keyword tool helps to search more genuine keywords people searching for.