Your main damage cooldown is Death Wish, which boosts your damage by 20% and gives you fear immunity at the expense of taking 20% more damage for 30 seconds. It has a 3 minute cooldown, so you’ll want to use it at times that’ll allow you to use it as many times in a fight as possible. Unless you specifically need to save damage cooldowns for a burst phase, you can use it at the beginning of a fight and on cooldown to maximize uptime.
The vanilla WoW Horde leveling guide you see on this site was originally made back in 2006 by Joana (AKA Mancow, or FuriousPaul).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.