You can confer some of your site's reputation to another site when your site links to it. Sometimes users can take advantage of this by adding links to their own site in your comment sections or message boards. Or sometimes you might mention a site in a negative way and don't want to confer any of your reputation upon it. For example, imagine that you're writing a blog post on the topic of comment spamming and you want to call out a site that recently comment spammed your blog. You want to warn others of the site, so you include the link to it in your content; however, you certainly don't want to give the site some of your reputation from your link. This would be a good time to use nofollow.
Expertise and authoritativeness of a site increases its quality. Be sure that content on your site is created or edited by people with expertise in the topic. For example, providing expert or experienced sources can help users understand articles’ expertise. Representing well-established consensus in pages on scientific topics is a good practice if such consensus exists.
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.

Google and Bing use a crawler (Googlebot and Bingbot) that spiders the web looking for new links to find. These bots might find a link to your homepage somewhere on the web and then crawl and index the pages of your site if all your pages are linked together. If your website has an XML sitemap, for instance, Google will use that to include that content in its index. An XML sitemap is INCLUSIVE, not EXCLUSIVE.  Google will crawl and index every single page on your site – even pages out with an XML sitemap.
Goals and Objectives. Clearly define your objectives in advance so you can truly measure your ROI from any programs you implement. Start simple, but don’t skip this step. Example: You may decide to increase website traffic from a current baseline of 100 visitors a day to 200 visitors over the next 30 days. Or you may want to improve your current conversion rate of one percent to two in a specified period. You may begin with top-level, aggregate numbers, but you must drill down into specific pages that can improve products, services, and business sales.