I think the biggest problem most people have is that they spend too much time doing not-leveling. It’s also the one thing that people do without realizing their doing it.
Basically what I mean is that any action you perform that does not work towards the increased level of your character is a not-leveling action.
There are tons beyond tons of examples. Some of them are preventable and others are not. The ones you can prevent are the ones you should focus on.
A lot of them are IRL. Getting the door, cooking food, feeding the cat, using the bathroom, spending excessive time doing necessary IRL tasks, changing your clothes, washing your hands, taking out the trash. In game: Checking the AH because you’re curious, spending too much time on bank alt, drawn out PVP engagements or battlegrounds, helping someone who isn’t on the same quest as you, stopping to type a long message.
By no means am I saying you should stop EVERY thing, because some things are just necessary and you have to do them no matter what. You can reduce the time it takes to do necessary tasks and you can eliminate unnecessary tasks.
Once you’ve found discipline outside of the actual leveling schedule, you can start to discipline yourself on the leveling routine itself. This is a bit harder, but it involves things such as efficient pulling and mana control. Never using more abilities than you need to kill an enemy (frost bolt the last bit of health or use the wand?)
How do I combat a lot of these pitfalls personally? I constantly remind myself, roughly every 5-10 minutes, to “focus on the goal”. I say this to myself the entire time while I’m leveling.
I don’t pull off record breaking 1-60 runs, I just don’t know the routes well enough to do that, and I also am victim of a lot of the things I mentioned. For example I will not be watching TV or listening to podcasts while I level in Classic. Why? Because I very easily get drawn into the movie/TV and forget I’m even leveling, to the point where I afk to the character screen before I realize I stopped. I also tend to google a lot of concepts I hear about in podcasts and that would steal time away from leveling.
I’m very easily distracted, and I realized in the end this was the number one thing preventing me from getting good leveling times.
Getting a good 1-60 time is as much about managing IRL as it is managing the in-game life.