SEOs put a lot of effort into link building – and justifiably so, since Google weighs links very heavily among the factors it considers when deciding where to rank a web page in its results. But the search engine doesn't treat all links equally, and neither should you. How can you tell whether a particular link is worth pursuing? Keep reading.
First, let me give credit where it's due: much of the content of this article comes from a thread started by PhilipSEO in our own SEO Chat forums. If you're serious about building links to your site, I recommend you read that thread, but be prepared to spend some time at it. Phil covers a lot more than just assessing a link's value, and many other SEO Chat forum members made valuable contributions to this thread as well.
Let's get started. If you want to climb the SERPs, you need to get links that are of high quality and permanent. These kinds of links “deliver the largest impact fastest,” Phil notes. So how do you tell whether a link meets these criteria? You'll need to start by assessing the page which will link to yours, based on several factors.
The first factor you should consider is relevance. Look at the page that is linking to your site. Is it relevant to the target page (the page that you want it to link to)? Is it relevant to the target page's keywords? Is it using relevant keywords in prominent places that Google will catch? Look for keywords in the following places, keeping in mind that you may have to use the View Source command when viewing the page through your browser to see some of them:
Title tag
Domain and URL
Heading tags (H1, H2, etc.)
Elsewhere in the text and HTML
Backlinks pointing to the page itself
The point is to check the areas that Google would look at to judge relevance, and see if they match your target page. So if you've just written the definitive article on how to groom your dog, and you hope to get a link from a site selling dog grooming supplies, you should be looking for phrases like “dog grooming,” “grooming your dog,” and so forth.
Search Optimization 
