I'm not exactly sure what you mean by an "evergreen niche" but as a general rule for generating traffic to a site in any niche, the best thing to do is post quality content that people will want to share. After you have written your quality content, send the quality content to 20 of the most dominant players in your niche. A back link from power players is sure to increase your traffic. After you send the original quality content to the 20 blogs, change 150-300 words of the article, maybe change the title, and send it to the next 20 blogs. Don't send the content to more than 20 blogs at a time because you'll be viewed as spam. Make sure you get the power players in your niche as well as the little guys. All the back links count as long as its from a reputable site, but of course the power players hold more weight. Also, try to get someone with influence to do a guest post and be sure to include a back link to their site. This will benefit both of you, more-so you because you're looking to increase your traffic and they already have traffic. Good luck.