For whatever it's worth, I'm a new player too. Level 54 Dragoon, just finishing up ARR.

I started out doing every sidequest I could find but I noticed by around Level 15 or so I was starting to outlevel the MSQ so I dialed back to just doing the MSQ and job quests. It took a bit but eventually the level of the MSQ "caught up" to me. I'm currently running Level 50 quests at Level 54, so still just a tad ahead but not so much it hurts the experience.

I'm starting to mess around with other jobs, and I plan to do sidequests then.