The starting principle is always the same: succeed in gaining quality inbound links, or also called backlinks, on other sites with high authority in order to make your website rise in the SERPs or search engine results pages. The inbound link is always a hyperlink that will point to a page on your site. In this context, it can be a link in a blog article, in a general or specialized directory, on an e-commerce site. The more the site on which you will have a link to one of your pages, will have a strong authority, measurable with tools like SEO Majestic or MOZ, the better it will be for your popularity. Other criteria can of course define the quality of a backlink. Is it placed in a hot area of the website, what is the nature of the anchor text, is it a link placed in a forum comment that could then be considered as spam, is the site on which you have a link to your site in the same theme as yours, etc.?