Within the context of Classic, the method most frequently proposed is to re-tune bosses to make them harder. Rather than copying the numbers, re-create the relative difficulty. Kind of like, when you first start working out, you use small weights. When you get stronger, you lift bigger weights. The WoW community is more knowledgeable, more experienced, has better hardware, etc. We're "stronger." So give us tougher bosses. There are a lot of forms that could take. Bosses were constantly re-tuned during vanilla anyway, so if Ragnaros does 10% more damage or something, is that really a problem? I don't think it is. What about resistance gear? back in the day, collecting resist gear was a thing people did. But the numbers and strategies are so well known today that only the tank really needs it anymore. Bosses could be re-tuned with more resistible elemental damage so that's important for entire raids to gear appropriately. That would be entirely keeping with the spirit of vanilla even if the actually numbers sitting in a database somewhere were different than they were ~13 years ago. If you want to go a little farther, a few people have proposed adding new abilities to old bosses, adjusting their timing, etc.
Different qualities aren't limited only to wild pets—many rare World drops and special non-wild companions have had their stats boosted. For example, the world-drop dragon whelps (Azure Whelpling, Crimson Whelpling, Dark Whelpling, and Emerald Whelpling) are of [rare] quality. Check your Pet Journal to see the color-coded rarity of your non-wild pets. 

A new quest will pop up once your first pet reaches level 3. It will send you to either Audrey Burnhep in Stormwind or Varzok in Orgrimmar. These trainers will offer a quest chain to battle specific Pet Tamer NPCs on each continent. Defeating each of these NPCs will reward a nice chunk of experience for your pets, as well a Sack of Pet Supplies (which has the chance to drop the Porcupette companion, among the always-useful pet bandages).
This is for those who want to own a piece of Vanilla WoW history!  This tier requires your physical mailing address so I can mail you the printed paperback binded mini leveling guide/book.  By default I will sign "Joana" on each book!  If you wish for me to write something else out (such as my real name) you can request that as well.  And finally, thank you for the support and I will continue to make the best leveling guides for WoW!
The vanilla WoW Horde leveling guide you see on this site was originally made back in 2006 by Joana (AKA Mancow, or FuriousPaul).  The guides have been tweaked many times over the years to make things "faster".  The leveling guides were made because of all the messages I got from people asking me how I was able to level up so quickly on new realms.  I was first to level 60 on 7 different realms (3 with Mancow and 4 with Joana), even winning Blizzard's "First to Level 50" contest they held back in 2006.
To me, certain character limits tend to be problematic not because of the length of actual content, but because of formatting tags and embedding taking up a lot of characters. This is something I experience on most of websites, not just this one, but the most aggravating issue over here is linking to user profiiles and other sources of strategies, which could be alleviated with internalisation of link paths and @mentions.
For example, the Azure Whelpling belongs to the Dragonkin family. However, it has Beast, Magic, and Elemental abilities in addition to a Dragonkin attack. Different attacks are strong and weak against different family types. Having a diverse spell selection might increase your chances of being prepared with a strong attack against an opposing team.
Zygor's Leveling Guide for The Elder Scrolls Online (PC Version) is an in-game, software based, strategy guide that will show you the quickest way to level your characters from 1-50. You can view and use the guide directly inside the game without having to print out anything or view the guide in a browser. This also means that our guides are dynamic and can track your progress in realtime.
When hovering over an ability, the tooltip will tell you whether or not that attack is weak or strong against certain pet types. Additionally, you can hover over the opposing team's pets and view their attacks during combat. This will be important since it’s a good idea to pit a pet that's strong against the opponent's pet who's vulnerable to that type.
Some quests in my guide are marked as "SKIP" and colored in red.  These quests are simply either too hard to solo or not worth the XP/time and are skipped.  My guide will only list SKIPPED quests if the quest is a direct follow up after completing a quest, not one that you have to click the NPC again to get it.  If you hover over the skipped quests, it will give info on why it is skipped in the guide (unless that info is already listed directly in the guide text).

One of my favorite features is the Smart Injection System, which automatically determines the optimal place for your character to get started with the guides, based on your level and quest history. In other words, it doesn’t matter what level you are currently, you can jump right in and continue seamlessly with the guides. It also means that you don’t have to be a slave to the guides, they work perfectly even if you’re also leveling in instances, battlegrounds, using heirlooms or rested EXP. If your level ever gets ahead of the guide, just use the built-in feature to skip to the right place again. Very cool.
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