In order to reach the top position on Google you must have complete understanding of 3 things
Optimization, PageRank and Backlinks.
Merriam -Webster dictionary define "optimize" : "Optimize- to make as perfect, effective, or functional as possible"

2 types of optimizations:
1. Onsite optimization
2. Offsite optimization ( optimization of backlinks)
Onsite Optimization- is the fine tuning of the website by the use of various tools such as meta tags, keyword density and many others. Correct onsite optimization ensures efficient and smooth ride to target.
Offsite or Backlinks Optimization- Backlinks optimization is the practice of making backlinks perfect, effective, or functional as possible. It is by far the most important function of the SEO. Getting backlinks without knowing that backlinks can be optimized is possibly the biggest omission in potential advancement of of the website.

What is a PageRank and how it is related to backlinks optimization
Google assigns a numeric weighting numbers from 0-10 for each webpage on the Internet; this PageRank denotes the site’s importance in the eyes of Google. It is also known as PR0, PR1, PR2, PR3, PR4, PR5, PR6, PR7, PR8, PR9 and PR10 with the purpose of "measuring" the webpage relative importance among websites. (A website can have different PR assigned to different pages within the same website.)
Google describes PR: PageRank relies on the uniquely democratic nature of the web by using its vast link structure as an indicator of an individual page's |importance. In essence Google interprets a link from page A to page B as a vote, by page A, for page B. But, Google looks at more than the sheer volume of votes, or links a page receives; it also analyzes inspects the page that casts the vote. Votes cast by pages that are themselves "important" weigh more heavily and help to make other pages "important".
A PageRank results from a "ballot" among all the other pages on the internet about how important a page is. A hyperlink to a page counts as a vote of support. The PageRank of a page depends on the number and PageRank metric of all pages that link to it ("incoming links"). A page that is linked to by many pages with high PageRank receives a high rank itself. If there are no links connected to a web page there is no support for that page.
The PageRank (PR) is derived from a theoretical probability value on a logarithmic scale like the Richter Scale. It means, for example, that a PR9 can be 10 times more valuable than PR8 and maybe 100 times more valuable than PR 7. The PageRank of a particular page is roughly based upon the quantity of inbound links as well as the PageRank of the pages providing the links. It is known that other factors, e.g. relevance of search words on the page and actual visits to the page reported by the Google toolbar also influence the PageRank. The name "PageRank" is a trademark of Google the exact formula that determine the PR is kept confidential by Google.

Backlinks, also known as inbound links, are the backbone key ingredients of Search Engine Positioning. Backlinks are links on other websites that lead back to your website. The more established, high quality, and high Page Rank the website that contains the link has, the more power it has to help the linked website with its search engine position. If the website that is getting backlinks gets many high quality links from high PageRank websites, it has better the chance of being in a high position on the search engines results page serp (search engines results page) .

Not all backlinks are equal there are other factors beside PR that determine the value of each links.

What is a quality link?
Any link that brings a benefit to your website can be considered "quality link" .Unless the link comes from "bad neighbored" it is to lesser or greater degree a "quality lead".
Backlink's quality is determined by:

The backlink PR value
The backlink's origination page content-relevancy in relation to your own webpage content
The backlink origination page's location in its website
The manner in which the link is showing
The number of outbound links on the origination webpage and other factors.

Optimizing backlinks is the skill and application of getting the most out of a link for the benefit of better position on a serp. At www.backlinkstrafficseo.com a system called "Power Backlinks" utilizes the fact that when backlinks are being optimized together to promote a single keywords it overall efficiency is so high as to place the key word on the top 3 position of Google serp. It is just like ordinary light turning into laser beam.
A race car with the most powerful engine will not win the race unless that engine is tuned up, in the same manner a non-optimized backlinks will not get you to the top of the search engine result page. When you correctly optimized the backlinks you will experience spectacular results.

How to optimize?