Start targeting long tail as well as short tail keywords,
You can use keyword tools to start analyzing different keywords.
Checkout google adwords keyword tool for a free alternative.
Otherwise I enjoy using Market Samurai( I know that they offer a free trial so you might want to look into that and see if its worth it for you)
You also need to makesure your onsite and offsite seo
are good (backlinks, no keyword stuffing etc)