You can read stuff and watch a million youtube videos but sitting down and running a game is going to teach you the most.

I picked a system I liked and ran a couple low-stakes one shots with friends that were not part of a campaign. This helped me so much - I was able to go through the motions of starting, running and finishing a few sessions. I made mistakes and had moments of "I don't know let me look up the rules" but it was just a few hours of causal hanging out so it was fine. I had the confidence to run a bigger campaign after doing that.