Once you've got rotations and specs down, the next most important thing at max level is gearing - stat priorities and caps, gemming, etc. But while you're levelling up from 80-85, that's not too important. Go to the practice dummies in Orgrimmar, and give them what-for until you're reasonably confident in your rotation and how your abilities interact with each other, then dive into some dungeons.
Your dps may be low. This will partly be due to inexperience, but mostly due to the fact that mobs die too quickly for you to get the full benefit of your rotation, so don't be discouraged by that. The rotations you'll see on sites like EJ are designed for raid bosses, which last a lot longer. Prioritise area of effect abilities on trash, and practice your main rotation on bosses. And, if possible, group with guildies who'll be happy to give you pointers specific to those dungeons, so you can concentrate less on what to avoid and more on using your class's abilities to the fullest.