New to the game. Tips?

Hey friends, just started playing and, for one, I can’t believe I didn’t get it sooner, it’s incredible. The most visually beautiful game I’ve ever played.

But second, I wanted to see if y’all had any tips for me to get the most out of the gameplay while I’m at the start. Would you recommend I just focus on main missions or go heavy into side quests or a little bit of both?

Any suggestions from seasoned folks would be appreciated!