Keep updating relevant articles and share them using social media platforms that could get improved organic traffic that eventually increases metrics of the website. Other way you could try adding high DA sites just make sure they are relevant to the niche as well!
DA can be increased by building various good quality backlinks to your site. So you should start immediately, create as many good backlinks possible and you should see some jump in DA/PA. But also note that it will not grow in few days it will take some weeks to months to reach to at least 20. For higher DA, you will have to work even harder and gain more and more backlinks.
Lastly, just the sake of clarification - merely increasing DA will not help your site rank high. You should also focus on creating good quality content by doing proper keyword research. Try to bring your site at the top of SERP for those keywords. DA will increase automatically during this process.