Link building and guest posting will help you to improve the DA of the site.
In starting you need to focus on increasing the number of referral domains and when you will have more than 1K referral domains then you can go for the other activities, For example, creating classified backlinks daily on high-quality sites.
To know more about it I have a great blog for you- https://www.ezrankings.com/blog/how-to-increase-your-websites-domain-authority/
Hope it will help you!
If you still have any queries then you can call - 9560133711
