You can youtube different methods, and they are all still highly relevant. I believe there's something called "method 0", which is basically boosting yourself by the use of instances. You don't even need a second account for it, but it'd make the process way easier obviously. If you don't have 2 accounts, just use some random person to form the party and have your 2 characters in the party and then kick / make the 3rd person leave afterwards. You then enter the instance on both your characters. You log on your low lvl and alt+f4. This acts as a "game crash" and will therefore not log out your character. You then log your high level character and run the mobs to your low lvl character and kill them. You'll be on a timer. Eventually your low level character will log out. Keep alternating between the 2 characters and slowly move your low level character more and more through the dungeon.
A quick way to level to the minimum requirements of entering the dungeons is to first do murloc camp at eastvale logging camp for 1-10 for alliance , worgen camp in one of the Undead zones, can't remember if it's in Silverpine forest or something 1-10. Spam dungeons after that.