I did this myself, and toward the end of BC my Druid was hitting 70. One thing I'd advise is to level tanky Feral, and to use the AoE capabilities of Feral for grinding/leveling. That will get you used to dealing with stacks of mobs at once. Try to solo a few of the small group quests in Zangarmarsh, there you should need to use defense cooldowns while keeping your damage up. If you can solo the Naga at one to two levels above him, you should be good. That one is kinda tough because you have to clear mobs, watch for pats, carefully pull him, position yourself to deal with his knockbacks, while also keeping up your DPS (your main method of aggro as a tank), plus, for his level, he hits pretty friggin hard, so you'll get used to working your defensive CDs. You can also try tanking the shard giants in Hellfire solo. They hit pretty hard, and the shardlings that split off can wear you down fast.

One you get up near 70 and have some decent tank gear I'd really recommend running a few Outland instances. Maybe once you hit 71 or 72 and have some Northy quest gear run heroic Ramparts. It isn't a tough run, but it is a pretty good place for a tank workout; you have lots of pats, mobs that stun, spellcasters, annoying los pulls, and the final fight gives you practice turning a boss while not standing in fire. Once you want to test your tankin chops, try heroic Shattered Halls. I'd lay good money that heroic Halls will be a tougher run than heroic UK or Nexus, even though your level and gear ilvl are higher than anyone had in BC.

By the way, the Naga quest I was thinking of was:
http://www.wowhead.com/?quest=9817
.. where you have to kill Rajis Fyashe