It is best to post your comments on dofollow blogs (Google will index your link.). Fortunately, we can use some tools to find these blogs. One good dofollow blogs search engine is the DoFollow Diver with over 700 blogs in its database. Here, blogs are categorized as dofollow, commentluv or top commenters enabled.
Some bloggers have compiled their own lists of tools and their own list of blogs.
Commenting on nofollow blogs is a waste of time when it comes to link building for Google page ranking. You need to be sure that your time is not being wasted by verifying yourself that the blog is indeed a dofollow. Note that a lot of blogs revert to nofollow after submitting to these dofollow directories. You can find a lot of nofollows at dofollowblogs.com.
Some ways to verify are:
1. The u comment I follow badge.
2. If you see a Top Commenters portion at the sidebar.
3. The commentluv badge or keywordluv badge.
4. Sezwho enabled.
If you're browser is firefox, just install the add on SEOquake. With this turned on, it will line through the nofollow links. you can also see the
PR of the site at the toolbar. Comment on high
PR sites.
For Internet Explorer, I've yet to see an add on for this (though I'm still looking for it.). What you can do is right click on the blog page, view source, edit, find rel="nofollow", or the meta tag will be nofollow, or the robots.txt may have disallow.
Remember, as a general rule, post worthy comments. Don't just type "Nice post. Thanks." or "Great information, thanks for sharing." While many still allow these kinds of posts, and you have successfully placed your link, the readers will never click on your link.
It is best to build relationships with the blogger and the readers to fully reap the benefits of your blog comment. Eventually, the blogger himself will notice and even link to your blog. Add value by participating in the discussion and sharing useful information.
Never spam.