The truth is whether you gain a link or not, if he comments on a blog post about dogs and his blog is about motorcycles its not doing any real good. So what is the right way. Lets go thru some.

Again, we are talking about targeting backlinks to a specific keywords or phrases on your page. Use Google blog search or a blog search tool and run it on your keyword. The more long tail or specific your keyword search phrase is the better because you will get posts targeted directly to the phrase. In other words if one of your keywords is "keywords", you are better of targeting a phrase more specific to the content on the page you want to link to, like "keyword density". Now, be sure that the page is actually optimized for this phrase or you are not doing yourself any good.

Now the search engine results from page one will hold a lot of relevance obviously, because they made the first page.

Now you can leave some quality comments on a few of the results and get better links. Remember, don’t just say "Nice Post" that does’nt leave a good taste in the moderators mouth and your comment stands a good chance of being deleted. Actually read the post and then make a valid comment, not that difficult.

The best scenario is that your comment can include HTML or at least links with anchor text. This is what you really want:   

ex. Thanks for the great info on keyword density etc. etc.   with the URL to your page being the link associated with your keyword phrase. This creates a backlink with your phrase or keyword as the anchor text a major plus. If you can only leave a link itself, make sure it points to the specific page ex: http://netfreeinfo.com/blog/keyword-focus-density-matters-blog/.