I personally just play the game. I tend to get a ton of XP from simply mining out ravines and caves. Killing any mob I see also gives quite I bit. I have played a world for a few days off and on, and I already have lvl 30.
Rollback Post to RevisionRollBack
My new survival journal is out! Come check it out here! All readers are appreciated!
I mine quartz in the Nether, which gets me to level 30 in 10-15 minutes; at 3.5 XP per ore it is really overpowered for its abundance, about as easy (if not easier) to find than coal in the Overworld (actually only as common as iron but it is exposed everywhere; ironically, even coal averages more XP (1) than iron (0.7), despite being more common).
This is also probably faster than spending all the time to make an XP farm, especially an Ender-Ender; I get all of my gear enchanted in a few hours before I even go to the End (though the only highly enchanted item I actually bring to the End is a Power V bow); it also helps to know that you can enchant books for 1 level to get Efficiency, Protection, Power, and Sharpness, then combine them to max them out, making it very easy to get those enchantments (particularly Protection on armor; do people really risk so many diamonds, or even iron, for a chestplate that might get Thorns or something? Combining books may cost more XP and anvil uses if you get lucky on the first level 30 enchantment but the overall costs are usually less).
Also, while you can't indefinitely do this (without eventually having to go very far away from the portal) I have no need for extra XP after I enchant my gear as normal gameplay gives me far more XP than I need for repairing (for example, the sword I use costs 35 levels or 1205 XP to repair, while it gives back 7800 XP from the mobs it kills, a factor of more than six, leaving plenty left to repair armor; even when I used an extremely expensive Efficiency V, Fortune III, Unbreaking III pickaxe for all mining I was able to get enough XP, while the XP I now get with just an Efficiency V, Unbreaking III pickaxe is absurd, 50-60 levels or even more before the next repair; and no, I'm not going to enchant just to avoid "wasting" XP when I have no need for more enchanted gear, especially since that means I'd have to stop what I'm doing and run all the way back home to enchant).