How can I improve conversion without user testing?

I work as a UI/UX designer. I have a good understanding of UI, but my UX is not as great. I spent a lot of time this week looking up topics on conversion, and ways to increase conversion rate. Most of the blogs sites I've been on, always relates back to the end user, which I understand.

My question is how to understand users with no user testing? Are there alternate ways that I can gather information on users, without doing user testing?

Also if there are any websites or references that might help with question that I have, please feel free to post them.

PS. My coding background is very basic.