Hi Yalina,

Use this link: http://wow.joystiq.com/cataclysm
to read up on the dungeons. I would try them on normal at least a couple of times, then jump into Heroics. I'd avoid saying that you haven't done it on Heroic. If anyone asks directly, just say you're rusty, it's been a while, you haven't played this toon since Wrath and you're still gearing up - whatever you're comfortable saying and which sounds plausible. (But seriously, do it on normal a couple of times.)

What you'll find in the pre-Zul Heroics are: guilds doing guild runs, people who just hit 85 and are gearing up, people like yourself who haven't been doing dungeons, and people leveling alts.

My personal advice would be use CC if you've got it, attack what the tank is attacking, and protect the healer. I know, it's stupid to say it, but really really important in the early Heroics. You don't have the luxury of wandering around, mining, looking at stuff like you did with Wrath (or in current Vanilla). Also - stick with the group. Some dungeons (Stonecore, I'm looking at you!) have weird little mobs that zerg in and kill the person who's at the back of the group. Don't follow at a distance.

Once you're ready for the End Time Heroics, use this link:
http://wow.joystiq.com/2011/11/29/patch-4-3-5-man-bosses-in-5-seconds-or-less/

Have fun, and good luck!