Here is a guide for beginners who wants to progress as fast as possible.[]
100% of the time: The deeper you go, the more XP you gain.
If you can find the stairs/portals to the deepest part of the dungeons, you will significantly improve your farming speed.
As I had to switch phones later on in the game, all I did was go to the deepest part of the dungeon, farm there and get better items and faster XP till I was ready to head to the next cave/section of the cave. Don't need to bother with exploring 100% of the cave unless you are missing an important item.
Also you don't need to bother with changing jobs unless you are trying to get high jobs or want more variety with your characters. I currently have all characters at max level 50 with base jobs 100% learned and will finish High Jobs in a few more hours. - Barrett. Level 41 Anotherworld Dimension