First, do not buy backlinks unless you do not mind losing the domain.
I had to reject so many "quality" backlinks purchased because they resulted in a penalty. Generally, they will qualify you before they penalize or de-index you. If you are in this for a long time, use some of the whitehat tactics below.
1. Complementary blog – follow and do not follow. Just make sure that blogs are relevant to the niche or at least that publication is relevant to your niche. Also be sure to make a contributing comment. Do not just make a comment like "good post" or "a good read". Also be sure to use your name or your name @ trade name, do not use keywords.
2. Web 2.0: Tumblr, Weebly, WordPress, Blogger are just some of the most popular. If you can get links to your Eeb 2.0 sites, they will be even more powerful.
3. Social bookmarks: there are a lot of these available. Just search in google.
4. Profile links – many sites will allow profile links. Most social networking sites and forums will have a place for a URL link in their profile.
5. Directory links – there are good and bad directories. Check the trust value before adding your business. The best ones will cost you, or you will have to pay to send them or they will send you an email and they will call you to update. These are critical for local SEO and for getting your NAP on the network. But it is not so valuable for organic SEO.
6. HARO: helping a journalist is a good way to find journalists and bloggers who seek professional advice in exchange for a back-link. Not all journalists will offer a link back and its content must be very good to be published.
7. Guest Blogs: There are many guest publication opportunities available. The content you write must be relevant to your niche and must be of high quality and original. Many times that content may be better on your website. I'll explain it to you in the next step.
8. Produce quality content: quality content is not just written content. Infographics, images, videos and written content can be shared and earn backlinks. When you post high quality content on your website, you should share it on as many social media platforms as possible to gain more links. Those who read it on social sites may link it again and hernia more backlinks.