There are actually 3 main things you should focus on, in case your site has lost rankings in the latest google update.
1. Guest Posts- Make good and unique guest posts on other blogs that are relevant to your niche. try and find some good ones with quality content and contact them asking to publish a guest post with your link.
2. Authority Backlinks- Press releases are my favorite, they tend to be indexed very fast and bring constant traffic. Other than that, authority backlinks consists of high PR links, edu/gov backlinks, video backlinks and more.
3. Social Signals- You must have a constant drip of links coming from various social networks. That gives an indication that your site is real and people are talking about it.
Hope this help you!!