You should equip new quest rewards when their item level starts beating out your previous set of gear. If you are currently wearing Tier 21 gear, it is best to let the quest rewards significantly beat your existing item level before using them. While a Tier bonus is worth a fair chunk of damage, the stats will quickly fall behind. Azerite gear additionally is another 1-3% per bonus, on top of raw stats.
The leveling path was built around using a Hunter character and run by a player who knew how to use that character well. For the average player running, for example, a Paladin, the guides could be frustrating in spots, due to the level of the mobs. I played through Joana’s Guide with a Rogue (all the way from 1-70) and was able to deal with most everything, except for a few elites and I skipped most all of the group quests.
The home page for the guide says that using it is like having a leveling guru giving you constant advice. Having used the guide for a quite some time now I’d say that’s pretty accurate. You’ll always know what to do and where to go next, automatically. Remember all those questions in the in-game trade chat, asking what to do or where to go next (for whatever level?) It won’t be you asking those questions.
-Azerite Gear- This has been the worst experience for many players as it was advertised as offering the player many options for customizing their character but all players do is Google "Icy veins (Spec/Class) azerite ranks" and select the best one. This is expected and really only gives players the illusion of choice as they're always going to pick the best one. This could have been done far better by not offering necessarily just damage increases in traits but offering some of the Legion Legendary item effects in Azerite slots. You know, certain Azerite traits would be better for PvP, some for raiding, some for 5 mans, some for soloing old content, etc. The other problem with Azerite gear is that it's locked based on you grinding an endless amount of Azerite for your neck piece (basically the stuff that increases the level of your neck piece). So when you get an item that should be an upgrade, it really isn't because you don't have all the traits unlocked. This complaint about how horrible this system is could go on forever, but I'll just leave it at that, horrible.
For Alliance it's Lok'Modan, Redridge, Darkshore, Felwood, Stranglethorn (both parts), Plaguelands. Somewhere between 3 - 3.5 of these get you to 60 in like a 16 hours /played, if you queue for dungeons at the same time. I recommend dropping everything at 45 and going to Darkshore-Felwood if you didn't do them yet - they are literally the fastest levelling zones in the game right now, maybe only trumped by Silverpine.
And, of course, there are plenty of in-game addons you can use to make your adventures in Azeroth even more efficient. Try checking out Azeroth Auto Pilot, which points you where to go, handles all your NPC discussions and quest turn-ins, and automatically sells your junk gear (among other features). Deadly Boss Mods is still a must-have, so you don’t die in dungeons quite so quickly. Pawn helps you tell whether the gear you’re getting is actually an upgrade or not. World Quests List gives you a much better way to see what’s happening in your zone (and sort for the rewards you’re prioritizing).
Waypoint System with Taxi Feature - Works similar to TomTom, clicking the Quest POI in your Objective Tracker will automatically place a waypoint for the quest. The waypoint arrow will turn green if you enter the selected quest area. You can also create your waypoint by CTRL + Right Click on your map and you can also link them together by holding SHIFT + Right Click on your map.
Heirlooms: Heirlooms are the best source of bonus XP for leveling. All slots can be gotten pretty easily now, except the rings. The time you need to spend to get the rings if you haven’t gotten a level 3 shipyard in WoW is way too long, so getting the rings is generally not worth it. Having all your heirloom gear will boost XP by 55%. Generally, you want heirloom gear with crit on for leveling as you want to kill mobs in a few hits as possible