Since title tag have importance in SEO but, however you can not add title tag in Blogger post while being in compose mode, so you need to edit HTML. The anchor text (the text on which link is suspended) and title tag (appears when a user hover on link) are two major text which describe the page (to which link points to) more than the page itself, so you should add title tag to images, links, flash and other media because it gives search engine to crawl content from each of them.
So, as I said that you need to add HTML attribute inside the link. For that you must know how a link tag looks like.
Without title tag
With title tag
<a href='http://moz.com' title='The Moz Blog'>MOZ</a>
When to use title tag
<a href='http://about.me/hamzadhamiya' title='More about Mohammad Hamza'>Mohammad Hamza</a>Now here title tag describes that what will be on the page the link points to.Or you can use the title tag for some design reasons like the below one: