Image Names and ALT Tags
For the benefit of search engines the Image file (photos) names should be descriptive words. They should accurately describe the image and if relevant should also use the page keyword.
If the search engines encounters too many broken links on a site they may deem that the site is a poor user experience, which can cause a reduced crawl rate/depth, and both indexing and ranking problems.
Page Load Speed
In 2010, page load speed officially became a part of the Google search ranking algorithm. For usability reasons, best practices dictate that a web page should load within 1-2 seconds on a typical DSL connection.
Sitemaps are a way to tell Google about pages on your site they might not otherwise discover. In its simplest terms, a XML Sitemap is a list of the pages on your website. Creating a Sitemap helps ensure Google crawl all your website pages.
Search engines crawl the web link-to-link and broken links can cause SEO problems for a website. When Google is crawling a site and hits a broken link, the content of your robots.txt file tells the search engine crawlers how they should visit your site.
Search engines do not like duplicate content as it leads to a poor user experience, content quality issues and even penalties from Google. If you have duplicate content, you need to do everything you can to eliminate it asap.
Does your www. redirect to your non-www or vice versa? If not you have a duplicate website that will be severely damaging to your website rankings.