1. Change the Metadata. Site -> Metadata and change the site description and keywords to something appropriate to your site.
2. Turn on Search Engine Friendly URLs. Site -> SEO. Make sure you rename the file htaccess.txt to .htaccess which is located in the base install of your Joomla site.
3. Turn on Log Search Strings. Site -> Statistics. This data is invaluable to find out what your users are interested in and cannot find on your site.
4. Turn off the WYSIWYG Editor. Site -> Site. The HTML that the editor creates is not very clean.
5. Delete any of the default Joomla articles and newsflashes and replace them with your own content.
6. Change the text on the links page to something more original. Site -> Language Manager -> Site Languages. Scroll down to the bottom and you’ll see the links text you will want to edit. In fact, you can edit all the language files here.
7. Install Community Builder. If you are planning on creating a community driven site, this component is a must.
8. Install the Joomla OpenSEF component. This component makes your URLs more search engine friendly.
9. Turn off the unnecessary fields on the Contact form. I usually turn off everything except for the email form. Components -> Contacts -> Manage Contacts.
10. Unpublish any unnecessary Modules, like Banners and Polls. Modules -> Site Modules.
Any other suggestions?