Google Recommendations

Although many of us already know this, here it is from the horses mouth.

TITLE tags and ALT attributes
Your title tags and alt attributes contain important information that Google uses when indexing your site. Descriptive information will give us good information about the content of your site. In addition, text contained in your title tag can appear in search results pages, and useful, descriptive text is more likely to be clicked on by users.

Title tags

First of all, make sure your title tags are descriptive and accurate, and that each page has a descriptive title tag. Consider the title tag a place to showcase the most important topic for each page. However, be careful not to add too many keywords, as this could be considered keyword stuffing.

Not so good:

Better:

Best:

To be avoided (may cause your site to be perceived as spam):

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Alt attributes

The alt attribute is used to describe the contents of an image file. It’s important for several reasons:

Googlebot cannot read text embedded in images. Therefore, alt text is a useful way to give Google information about an image.
Many people, for example users with visual impairments, or people who use screen readers, or have low bandwidth connections, cannot see images on web pages. Descriptive alt text provides these users with important information.

Not so good:

Better:

Best:

To be avoided (may cause your site to be perceived as spam):