Moz invented these metrics and here is what they say:
How do I influence Domain Authority?
Domain Authority is difficult to influence directly. It is made up of an aggregate of other metrics (
MozRank,
MozTrust,
link profile, and more) that each have an impact on the authority score. This was done intentionally; this metric is meant to approximate how competitive a given site is in Google search results. Since Google takes a lot of factors into account, a metric that tries to calculate it must incorporate a lot of factors as well.
The best way to influence the Domain Authority metric is to improve your overall SEO. In particular, you should focus on your link profile — which influences MozRank and MozTrust — by getting more links from other well-linked-to pages.
Source:
https://moz.com/learn/seo/domain-authority
How do I influence Page Authority?
Like Domain Authority, Page Authority is a holistic score and difficult to influence directly. It is made up of an aggregate of metrics that each have an impact on the score. This multi-factorial dependence is intentional: Since Google takes a lot of factors into account when ranking a page, a metric that tries to calculate it must incorporate a lot of factors, as well.
The best way to influence a page's Authority is to improve its link profile, which influences its MozRank and MozTrust scores. This can be accomplished by getting
external links from other high-authority pages, which in turn act as "votes of confidence" for the authority of your page.
Source:
https://moz.com/learn/seo/page-authority