Well, domain authority simply defines how authoritative your website is.
I'm sure you are familiar for "Apple Authorized Reseller". This simply means people can trust the store and buy their needs without any chances of theft.
That's the reason why Google and other search engines tends to rank website with better Domain Authority; because users trust authority websites. So, now that you understand the "Why" behind increasing, you need to understand the mechanism of increasing authority of your website. To make your website authority, you need to focus of 2 major things: one-CONTENT and two-Backlinks.
Assuming that your website already has quality content, you need to focus more on building links to your website. More links means more trust. It is also important that you build links to your website from Domain Authority higher than that of your website.
For instance, if you website has a domain authority of 7, then you need to build links from domain authority of more than 10.. higher the better. BUT, with a domain authority of just 7, you cannot aim directly in building links from very high domain authority like 50+ because it difficult and people might not be interested in giving you links.
So, here the deal:
Month 1, Month 2 and Month 3 – Focus on building link from DA 15 to DA 25
Month 4, Month 5 and Month 6 – Focus on building links from DA 25 to DA 35
Month 7 to month 12 – Focus on building links from DA 35+
Types of links to focus: Contextual
Hypertext: 60% keywords, 40% brand keyword.
I know what you're thinking... 1 YEAR....! haha... White hat SEO is a marathon, not a sprint.
All the best...!