What muscle groups should I work on?

I’ve been casually working out a couple days a week for years but want to get more serious and focused. I’m around 5’10” 162lbs in this photo. While one of my goals is a bigger and more defined chest, what muscle groups would you recommend working on based on where I’m at today?

I’ve been casually working out a couple days a week for years but want to get more serious and focused. I’m around 5’10” 162lbs in this photo. While one of my goals is a bigger and more defined chest, what muscle groups would you recommend working on based on where I’m at today?