Dear friend you should first do keyword analysis by watching global search,monthly search, you can get good keyword. You always choose that keyword from which more visitors come.
First you go to Google Adwords Keywords Tool and check the relevant and low competitive but popular keyword for your site and then use those keywords in the content writing of your website and in the Meta Tags and Submissions.
for finding best keywords for website is google keywords tools, but one more is google adwords where you can also find correct keywords for your website.