From my < 1 week experience
Never Solo, always team up
After 10+ be in a party, and fate farm, after every 10 levels go bum rush all main quest, side quests, do a few good xp guildleves
I made the mistake of soloing and wasting time in Phase 4
Party and FATE's go hand in hand
If you FATE farm, kill mobs around you in bunches, just keep being on the hunt, get XP
Don't wait for FATE's to pop, just keep at it
I think I got 5 levels from FATEs and 3 from just basic mobs getting obliterated and stacked, killing everything in sight
Whatever your level add +5 and kill those, have 4+ party member go to work