When you look for an influencer to partner with, look for someone who not only has a large following, but is knowledgeable and authentic. Give them any resources they need to clearly communicate your brand and what you do. When they post on social media, share their posts on your business page. Try to cultivate long-term relationships with influencers.
To do this, I often align the launch of my content with a couple of guest posts on relevant websites to drive a load of relevant traffic to it, as well as some relevant links. This has a knock-on effect toward the organic amplification of the content and means that you at least have something to show for the content (in terms of ROI) if it doesn't do as well as you expect organically.
Email marketing is an incredibly useful tool in a variety of ways. It helps you build a stronger relationship with your core audience, and lets you easily market new products or promotions. You can also share news and interesting information with your subscribers, and let them know about new content right away. All of these can have a significant effect on your traffic levels.