Cookies testing:

Cookies are small files stored on user machine. These are basically used to maintain the session mainly login sessions. Test the application by enabling or disabling the cookies in your browser options. Test if the cookies are encrypted before writing to user machine. If you are testing the session cookies.

Validate your HTML/CSS:

If you are optimizing your site for Search engines then HTML/CSS validation is very important. Mainly validate the site for HTML syntax errors. Check if site is crawlable to different search engines.

Database testing:

Data consistency is very important in web application. Check for data integrity and errors while you edit, delete, modify the forms or do any DB related functionality. Check if all the database queries are executing correctly, data is retrieved correctly and also updated correctly. More on database testing could be load on DB, we will address this in web load or performance testing below.

Test for navigation:

Navigation means how the user surfs the web pages, different controls like buttons, boxes or how user using the links on the pages to surf different pages.