Grinding is finding a spot with fast respawning mobs and killing them solo or duo more is waste of xp over and over again and yes so far its the fastest way to lvl up.
Do all the quests, world bosses, dolmens, and dungeons in a zone, then move on to the next zone. Basicly kill near everything you meet outside of cities and towns.
"We have found a cave, but I don't think there are warm fires and friendly faces inside."
Quests should be yellow or orange or red for maximum XP reward at the end , white gets no XP green gets you bare minimum
Playing on console nearly all my quests are always shown as green, some times yellow never seen red or orange. No wonder it takes me so long to level
Me? I'm dishonest, and a dishonest man you can always trust to be dishonest. Honestly. It's the honest ones you want to watch out for, because you can never predict when they're going to do something incredibly... stupid.
-Johnny Depp
Are you trying to get to max level or stay on level with the content?
If the former, find grind spots and kill mobs. If the latter, just do the content, you will be on level or even over leveled if you do most of a zone as you go through it.
Enjoy the game, life is what you really want to be worried about.
PakKat "Everything was going well, until I died"
Gary Gravestink "I am glad you died, I needed the help"