When establishing authority in Google’s eyes there are two main categories to consider.
1. Content
2. Back Links
The content requirement is common sense, after all the content is what a customer searches for and clicks to obtain. If you can provide exceptional content then you have satisfied more than half of the equation. But, depending on the key words, exceptional content alone may not get you to Google page 1.
The other 40% of the equation will get you on Google SERPs page 1 and that 40% is Back Links. My opinion is that Google uses back links as a measure of the value of a websites content . If other websites link to your content, and this is a key, link to your content and not just your website, then that is an indicator that your content has value. The key to getting quality back links is quality content. It seems to always go back to value which is your content.
Important considerations in back links.
First, back links should be for a specific keyword or key word phrase. This is an important point. Make sure the anchor text on the linking website includes your desired keyword or phrase. Provide the anchor text to make it easy for the other webmaster.
Next make sure that the link points to a page on your site that is about that key word or phrase, something like a landing page. The anchor text amplifies and points to the key word phrase on your site.
Third, the page rank of the linking page will determine the value of the back link.
Internal Links - Internal links are hypertext links within your website. Internal links are important for SEO because you can’t control the anchor text that other sites use, you can’t control which pages they link to on your site but you can control your own. The Internal links help to organize your site but also point incoming links to key words that you choose to emphasize. A site back linked to your website using anchor text for “blue widgets” may link to your main page. If your main page has a hypertext link to a full page on your website about and describing “blue widgets” then the focus on that key word is achieved. The Search engines will note that path for future reference and your search results will improve somewhat.
Make a list of the pages on your site that shows the keywords on each page for which you want to rank. Then review each page for opportunities to create an internal hypertext link. The list also is helpful reference when writing new exceptional content pages.
For more information take a look at Link Building and How to Build Quality Links for Free