Google introduced a suite of new features to Blogger.com, enabling you to more effectively customize your search preferences. "While most of the new features are located in the Settings tab, a few others can be found in the post editor. For example, the ability to incorporate "alt" and "title" tags to images in your post," Google stated.
Here's an overview of what is added:
The first thing you'll notice is a new "Search preferences" option under the "Settings" tab. Clicking it'll display three sub-sections: Meta Tags, Errors and Redirections, and Crawlers and Indexing.
Now you can edit the description meta tag without editing the template. If you edit the description meta tag for the entire blog, you can also write descriptions for your blog posts. This is useful because Google's snippets sometimes rely on this meta tag.
When enabled, some of these features, such as Search Description and Custom robots header tags will also appear in the "Post settings" area of Blogger's post editor as well. For example, if you elect to create a Search Description, you may do so for your blog, and/or individual posts.
Second, for the first time, you can add a custom "Page Not Found" (eg. a "404") message, and Custom Redirects for pages on your blog. Just "enter an HTML message that will be displayed on the Page Not Found page instead of the generic message." You can refer the following help center article for creating useful 404 pages and there's even a widget powered by Google search that shows related links and a search box with appropriate search suggestions.
Google also added a new "rel=nofollow" link attribute in the link tool. Checking this box means that you don't want this link to be considered when web crawlers are searching for information they'll use to index your page.
While most of these features are easy to understand and use, others, such as custom robots header tags are geared toward advanced users only, hence the warning message:
There are also options for customizing the robots.txt page and robots header tags. It's probably a good idea to use Blogger's robots.txt page as a template (http://yourblog.blogspot.com/robots.txt) and only add some new pages you want to be ignored by search engines.
Before diving in, read this quick Help Center articles.