In my opinions, there are several factors that will affect your domain authority:
1) The age of your domain. The older it is, the higher authority your domain will be.
2) The backlinks of your domain. The more, the better (Note: We should focus on the relevant and high quality backlinks.)
3) Let your website become popular, that is, traffic! The more visitors who come to visit your website, the higher authority your website will be.
I have just stated my own opinions, hope it will give you some inspirations.