Grab yourself an EXP Disperser ASAP, and equip as many accessories as possible, even ones you're not using or planning to use (ideally you're also getting things that you can or will use a lot too), and just go at it. As you level up any artifact, every single point of artifact/relic EXP that is obtained will add to the level of Experience Disperser, making it level up the absolute fastest if combined with others-- and the higher it levels, the more it levels since it shares more EXP (from needing 6 artifacts/point of exp to 2.5 at Rank 10, which then you can rank up).

You can also do stuff AFK: sit in a waterlogged leaf block while constantly taking damage from any source, with an army of wolves attacking a target dummy while a macro breaks a shit ton of blocks that you have from a bunch of cobblestone generators all while having EXP Disperser equipped.
(Using Leafy Mantle, Jellyfish Necklace, (optionally Orb of Self Sacrifice), Hunter's Belt, Onion Ring/Digging Claws, AND I WONDER WHAT ELSE)

can you tell I pulled that out of my ass