For link building, you need to build good relationships with your niche people. You can do it with posting on communities, forums, writing answers for users, blogs, social groups (Facebook, LinkedIn and Google+).
Add blog section on your website. Focus on your niche business and on your client’s needs. Write posts on a regular basis having relevant, useful and well-structured content.
You can also go for guest posting and find sites and blogs that will accept and publish your article, choose right blog or website relevant to your topic, focus on quality, reputation.