Unfortunately you can't guarantee great rankings for your charity's website, at least not straight away.
Search engines provide little information about how they decide rankings to stop people from cheating the system. However, a lot has been worked out by webmasters through observing the results of changes made to pages.
For example, I saw first-hand how popularity within search results makes a difference when I created a backpacker hostel review site a few years ago to promote my book on backpacking. Even though the site only had a limited amount of content and received few incoming links, its web ranking shot up and was eventually listed first in the search results for most of the reviewed hostels. The popularity of the site was probably because it held genuine and honest reviews, which web surfers could see from the snippet displayed by Google.
However, it took almost a year to reach this point, so be patient when doing SEO work for your charity's website. Search engine rankings should improve if you follow the steps below, but it will take a few months for you to notice the changes.
If you struggle to notice any improvement, then contact me - one of the services I offer is search engine optimisation.