There's tons of good articles here at Daniweb (do searches at the top right of any page) explaining different aspects of search engine optimization. You'll find out about things you can do to your web site to improve your rankings. They'll be things off site you can do to help boost your position in the search engine results pages. SEO isn't about one technique or thing you can do or one tag you can tweak. Sound SEO involves working several fronts.
Active? Is you site in WP? if yes that you mean to say how you install SEO plugin? if not and you want to do SEO for your site then you must start learning from on-page seo then you can go with off page which is easy.