When you have finished your quests and leveling in the 62nd level, you can head to the Zangarmarsh, or you can go to two instances better for leveling, both located at Coilfang Reservoir: The Slave Pens and The Underbog.
Level 64 brings you a new rank of Flamestrike and a new offensive spell: Arcane Blast, together with Amplify Magic, Arcane Missiles, and Frostbolt. The details about the use of the Frostbolt, you can see my last introduction focusing solely on spells. Actually, there are multiple ways to do it, but the basic strategy is to start your rotation with an Arcane Blast, which gives you a debuff that makes the next one cost 75% more mana but have a shorter cast time. The debuff lasts 8 seconds, giving you time to sandwich in some other high-damage spells of your choice, such as Fireballs, Scorches, Arcane Missiles and so on.
At level 65 you should probably be well into questing in Terokkar Forest, or even Nagrand. The instances for this level range are found in Terokkar, at Auchindoun: Mana Tombs and Auchenai Crypts. I strongly recommend that you pay an adventure to the Nagrand, even with your unfinished quests. The quickness and swiftness to arrive there may promise you a quest chain there called The Ring of Blood. This chain involves a 6-quest series of 5-man boss fights in an arena located in northern Nagrand. It rewards you with a ton of experience points, a lot of wow gold, and a hefty windfall of potions, as well as your choice of very nice weapon rewards. The reward will accompany you to the final destination; therefore, you should obtain it by all means and keep it. A good group can iron this chain out in a very short amount of time, however, when you come to the final allocation you can't argue with the rewards it offers.
As other new levels promise, level 65 will also support you with the new spells of Cone of Cold, Conjure Water, and Scorch. All these spells have their special traits when cast to enemies.