I'm having a hard time figuring out what I can/can't do in this game. Currently, I'm level 12 and I just got to Diamond City. My main problem is I really don't have any direction. Should I continue doing quests or just explore? Which quests? My main fear is that if I choose to explore I'm just going to get to difficult areas and not be able to progress at all. I'm also having a lot of trouble finding side quests. Where are all of these located?

Joining factions will give you tons of side quests to do which involves cleaning places of enemies to establish settlements and fetch quests to support their cause.

I'm currently doing quests for the minutemen and the brotherhood of steel faction. Easy money and tons of exp... I normally look for higher level enemies because they generally have some pretty sweet loot. Sure its an ammo waster but its worth the grind IMO.

Go tackle stronger enemies. You'll find the best loot that way and you'll level up faster. Go anywhere but engage methodically and sneak as often as possible. Having a sniper rifle helps in chipping enemy health from a safe distance in the out doors

Edit* If indoors especially with ghouls I carry a shotgun and my upgraded 10mm pistol

When in doubt, follow the MQ.