I do not recommend going for TBC, although I remember Hellfire peninsula to be decent, everything else is rather slow. Instead go for WotLK, Borean Thundra gets you levelled very fast, and then you can head straight for Icecrown at 67, which is also insanely fast, although admittedly has a few elite quests. You can go to Sholazar Basin alternatively. 2 zones should get you 60-80 no problem.
Havoc in Battle for Azeroth has gone through somewhat of a maturing process, trying to focus more on the talent tree and allowing for more diverse options in gameplay approaches, alongside tightening up some of the more loose aspects of the original implementation. It still remains a predominantly builder spender style rotation and is largely Global Cooldown locked. The core hook is making the most of your Fury pool and reacting to unpredictable gains, ensuring you use high burst cooldowns and windows to push yourself even further. On top of that, it comes with a variety of mobility and defense tools, creating a versatile toolkit with some unique abilities that can be used in a variety of ways.
If you need the abridged version, because you’d rather spend an hour in a game than hearing someone talk about a game, you can also check out the excellent “New & Returning Player Guides” series from YouTuber (and World of Warcraft expert) Bellular. And you probably even skip the bits about ”how to purchase” or “how to install” the game, saving you even more time for new World of Warcraft adventures:
These stat priorities help to get a rough idea of what gear to go for, but the most important thing to get as soon as possible is your stat weights. Stat weights help you zero in on which stat is the most effective at increasing your healing. However, healers have no grand simulator, as there are a lot more variables that can affect your overall performance than there are for DPS specs. In light of that, healers use fight analysis tools like WoWAnalyzer and the Teachings of the Red Crane spreadsheet that takes logs from WarcraftLogs and gives you accurate weights that would improve your output.
For reference, my previous best time abusing Method-0 in 7.3.5 was 32.4 hours(as show in the old thread). A difference of just over 8 hours; which isn't all that bad, all things considered. And I believe I made several errors along the way, which could be cleaned up in future runs. I believe that that gap could be significantly closed by using a monk's bonus, but I hate playing monk...so...yeah. YMMV