As well as optimising the way your website is programmed you should also ensure that your site is being linked to from other sites as this will boost your search rankings. In particular search engines are looking for links from reputable, high quality sites. If you want to find out how many sites are linking to your site just type link:www.yourwebsite.org into google. This will bring you back a page of details on who is linking to your site, you can use this to help identify organisations you already know that you could ask for links.
You can also try the following;