The first way to get contextual back links is to be a guest blogger on the site owned by somebody else within your topic area.  Preferably, they will have a highly ranked site, page rank three or better or be on the first page of Google for the keyword that you wish to rank.  There are a couple ways to find such guest post opportunities.

a.  Use the Google search function for blogs by typing your key phrase.  Click on the first 10 blogs that show up, comment on that blog site and if they have a contact link, asked the site owner about guest post opportunities.  The comment you leave will have some value even if the blog is a no follow blog as most are as explained in this post.

b.  Do a search on the phrase “guest blogging” or “guest posting.” You will find sites that have a list of other sites which are known to accept guest posts.  You will also find some networks that are designed to match guest bloggers with blog owners who desire to have guest posts.  Most of these networks have a free subscription option although they offer more features with the paid subscription.
The beauty of placing a guest post is that it will be specifically related to your topic and the SEO juice from that link will be of the best quality available.

Your next opportunity, similar to guest posting, is to place posts on Web 2.0 sites that will always accept your content.  These are sites such as WordPress.com, LiveJournal.com, tumbler.com and several hundred others:

http://www.wordpress.com/
http://www.tumblr.com/
http://www.livejournal.com/
http://www.blogger.com/
http://youblog.net/
http://myanimelist.net/
http://www.barnculture.com/
http://campusbug.com/
http://www.nexopia.com/
http://blog.com/
http://www.migente.com/
http://bravejournal.com/
http://www.getjealous.com/
http://xanga.com/
http://www.thoughts.com/
http://insanejournal.com/
http://webs.com/
http://www.blogcatalog.com/
http://newsvine.com/
http://www.geckogo.com/
http://posterous.com/

Once you create accounts at each of these Web 2.0 sites , you can either get software to do the posting for you or you can hire someone at fiverr.com to do it.

Similar to the above is to place your guest post articles on article sites such as ezinearticles.com, goarticles.com and many others.  Since anyone can place content on Web 2.0 sites and the article sites, one would have to conclude that Google doesn’t give too much value to these links.  However, you get some value and these links won’t hurt you.  These links won’t hurt you if in fact you have a complement of back links from high quality sites with authority.  If you have only these low-quality or low page rank links, they are likely to be of very little value in total.  In other words, Google sees it as normal that a site with 20 really good quality back links might have 500 common links from low ranking sites.  But if you have links from ONLY low ranking sites, these links will be of little SEO value.

Next, you can use automated services to basically do the above function and save you a lot of time.  These services vary in quality.  At the low end, are services like Unique Article Wizard.  Many of their posts go on sites rank PR zero or maybe PR one.  Therefore, it is best to use this site like unique article Wizard for second-tier back links, a topic we will cover in another post.  When Google sees your back linking profile is heavily weighted toward low ranking sites, the amount of page rank benefit you get is limited.  However, these posts don’t hurt you and the fact that they are automatically placed means you spend very little time creating these back links.

The better quality services, such as BacklinkMetro, will place your posts on sites with page rank 1 to 5 so that the quality of the back links you receive is better providing you more SEO benefit.

Last, are simply to place comment links.  To get back links from comments that will actually impact your search engine rank, you need to place your comments on do follow blogs.  If you do a search on the phrase “do follow blogs,” you locate those sites that pass link juice from their comments.  However, also place comments on no follow blogs because if Google sees comments from only do follow blogs, they see that you are trying to manipulate their system solely to win the search engine ranking game.  Make your comments worthwhile and make sure that your back links go to posts of yours that add value to the post on which you are commenting.  This will give you maximum chance of having a reader who is also a blogger link to your site or possibly even contact you about a guest post opportunities on their blog.