Lots of good advice in the reply above; a few additional pointers:
Thels wrote:- Blacksmiths can craft an ilvl 450 tanking set with ilvl 463 shield. They can also craft ilvl 476 Chest and Gloves, if you have the gold for it, or ilvl 496 Chest and Gloves with Raid drop recipes and Raid drop mats. For the 476 and 496 chest and gloves, consider if you want the Tank or DPS ones, considering we love Haste now.
In the end, I crafted bits of ilevel 450 pvp gear - with the new stat priorities, it was often better for tanking than the tank gear. (We like hit, expertise, haste and mastery better than parry and dodge; it's only crit we don't like and some of that can be reforged. The resilience and pvp power are off the item budget.)
Bear in mind that if you complete the final two questing zones, you'll get a number of 450 level blues, so you won't need a complete crafted set.
450 gear is really just to get you comfortable for dailies and heroic 5 mans. You'll want better to get into LFR and raiding. As Thels says, you basically want 463 drops.
Theoretically, your failsafe is JP gear, 458, which you can upgrade. However, I found JPs rather scarce this expansion, so I would advise you to save them and use them to upgrade a key piece of 463 gear down the road.
Instead of JP gear as a failsafe, consider honour gear. Tol Barad gives 800 honour for a victory+weekly quest; 500 honour for a victory. You can quickly rack up a lot of honour that way - enough for a piece or two of 458 pvp gear. I wanted a meta-gem and a cloak, so got them iirc. The honour gear is only a tad below the 463 dungeon drops but unlike them is failsafe. You can also upgrade to 466 by spending 1500 honour.
Finally run the world boss Sha of Anger each week. Loot it once and you get 476 boots via a quest. And once a week, you get a chance of tier 496 legs or gloves, plus a lot of nice 483 arena pvp gear. I would advise using a coin from your daily quests to get a double chance of a drop, as this is about the best pre-raid gear you'll find. (ok, technically, it is a world raid boss, but it's so casual - people are not screened in any pugs I've seen).