At one point, backlinks developed a reputation of damaging a site’s credibility through search engines. This is due to “black hat” SEO practices would add 5,000 links to a website overnight (a practice that is still used today). While the website would launch to the top of search ranking results for a few weeks, it wouldn’t stay there, and the site’s credibility would be damaged because a few dozen servers with thousands of useless websites existed for the sole purpose of creating backlinks.

PageRank is a link analysis algorithm and it assigns a numerical weighting to each element of a hyperlinked set of documents, such as the World Wide Web, with the purpose of "measuring" its relative importance within the set. The algorithm may be applied to any collection of entities with reciprocal quotations and references. The numerical weight that it assigns to any given element E is referred to as the PageRank of E and denoted by {\displaystyle PR(E).} Other factors like Author Rank can contribute to the importance of an entity.
Chris_D, great question. If you have a single product page that can have multiple urls with slightly different parameters, that’s a great time to use a rel=canonical meta tag. You can use rel=canonical for pages with session IDs in a similar fashion. What rel=canonical lets you do is say “this page X on my host is kinda of ugly or otherwise isn’t the best version of this page. Use url Y as the preferred version of my page instead.” You can read about rel=canonical at Bear in mind that if you can make your site work without session IDs or make it so that you don’t have multiple “aliases” for the same page, that’s even better because it solves the problem at the root.

Hemanth Kumar, a good rule of thumb is: if a link on your website is internal (that is, it points back to your website), let it flow PageRank–no need to use nofollow. If a link on your website points to a different website, much of the time it still makes sense for that link to flow PageRank. The time when I would use nofollow are when you can’t or don’t want to vouch for a site, e.g. if a link is added by an outside user that you don’t particularly trust. For example, if an unknown user leaves a link on your guestbook page, that would be a great time to use the nofollow attribute on that link.
If the algorithm really works as Matt suggests, no one should use nofollow links internally. I’ll use the example that Matt gave. Suppose you have a home page with ten PR “points.” You have links to five “searchable” pages that people would like to find (and you’d like to get found!), and links to five dull pages with disclaimers, warranty info, log-in information, etc. But, typically, all of the pages will have links in headers and footers back to the home page and other “searchable” pages. So, by using “nofollow” you lose some of the reflected PR points that you’d get if you didn’t use “nofollow.” I understand that there’s a decay factor, but it still seems that you could be leaking points internally by using “nofollow.”
Another tool to help you with your link building campaign is the Backlink Builder Tool. It is not enough just to have a large number of inbound links pointing to your site. Rather, you need to have a large number of QUALITY inbound links. This tool searches for websites that have a related theme to your website which are likely to add your link to their website. You specify a particular keyword or keyword phrase, and then the tool seeks out related sites for you. This helps to simplify your backlink building efforts by helping you create quality, relevant backlinks to your site, and making the job easier in the process.
A breadcrumb is a row of internal links at the top or bottom of the page that allows visitors to quickly navigate back to a previous section or the root page. Many breadcrumbs have the most general page (usually the root page) as the first, leftmost link and list the more specific sections out to the right. We recommend using breadcrumb structured data markup28 when showing breadcrumbs.

Search Engine Optimization