New to tanking... DK
As the previous post stated, there is a metric ton of this info out there and the best tanks read most of it, lol. Those are nice links and I agree they are a good place to start.
Having said that, it sounds like you are just making the dk and those have a lot of important general info that is true at any level, they don't have much non-level cap specific info. Here's a few thoughts:
Frost spec: good defensively and a little less gear dependant due to talents. Easiest aoe aggro so less frustrating while learning. Drawback- most level capped dk tanks are blood for the EH advantage which might mean learning a new rotation at 80 (not saying frost isn't viable)
Blood: random healers are...random. If you tank as you level (which I highly recommend) you will get some bad/undergeared/dps pretending to be healers. Blood's self healing can be nice but you will work harder for aoe threat.
Getting 5/5/5: this is the defining trait of a dk tank, however, it is not make-or-break for Ramps. Going frost, for instance, you might put your priority in getting howling blast at 60 and finishing 5/5/5 immediately after. If you do so, remeber you are putting more faith in your healers. For the added aoe convenience.
"he doens't need healing, he doesn't need healing, he doesn't nee-WHAOSHIT!wtf was that man!". Please stop leaning on TDR. -Teng