Suitable anchor text makes it easy to convey the contents linked
Anchor text is the clickable text that users will see as a result of a link, and is placed within the anchor tag <a href="..."></a>.

<a href="http://www.brandonsbaseballcards.com/articles/ten-rarest-baseballcards.htm">Top Ten Rarest Baseball Cards</a>

This text tells users and Google something about the page you're linking to. Links on your page maybe internal—pointing to other pages on your site—or external—leading to content on other sites. In either of these cases, the better your anchor text is, the easier it is for users to navigate and for Google to understand what the page you're linking to is about.

Choose descriptive text

The anchor text you use for a link should provide at least a basic idea of what the page linked to is about.
Avoid:

• writing generic anchor text like "page", "article", or "click here"  
• using text that is off-topic or has no relation to the content of the page linked to  
• using the page's URL as the anchor text in most cases                                                                         -  although there are certainly legitimate uses of this, such as promoting or referencing a new website's address

Write concise text
Aim for short but descriptive text-usually a few words or a short phrase.
Avoid:

•  writing long anchor text, such as a lengthy sentence or short paragraph of text 

Format links so they're easy to spot
Make it easy for users to distinguish between regular text and the anchor text of your links. Your content becomes less useful if users miss the links or accidentally click them.
Avoid:

• using CSS or text styling that make links look just like regular text

Think about anchor text for internal links too
You may usually think about linking in terms of pointing to outside websites, but paying more attention to the anchor text used for internal links can help users and Google navigate your site better.
Avoid:

• using excessively keyword-filled or lengthy anchor text just for search engines  
• creating unnecessary links that don't help with the user's navigation of the site