Enchanting like gemming is an easy way to go the extra mile to get your gear the best it can be, so you can keep aggro without dying or top the damage meters in your next Naxx raid. Since there is so few enchants available, it's a lot less complicated than gemming too. DPS will just want hit to the cap and AP, while tanks will want defense to 540 and stamina.
   Note that almost every slot with enchants has a weaker version and a more powerful version. In the case of enchants, it is OK at the entry level to go with the weaker version of enchant though it's usually frowned upon to go weak when can go strong. The more powerful ones generally take Abyss Crystals and the like, and may be a bit steep. Additionally, there're a few other quirks and special enchantments to watch out for. Let's take a look at some of the best choices for enchanting for both DPS and Tanking.
   The first one is weapon. Runeforging is better than enchanting, just to get that out of the way. There's no use wasting shards and dust on a weapon enchant when a better one is just a Death Gate away.
For DPS, it's very hard to go wrong by just applying Rune of the Fallen Crusader. The health will help soak up environmental damage, and strength will translate to AP, which will translate to spellpower, meaning that a large overall boost to your damage. Even better is the fact that it scales, meaning the better your gear gets, the better the proc gets. If you're running a Howling Blast build, you might get away with Razorice but otherwise, there shouldn't be any question in your mind that Fallen Crusader fits the bill.
Tanking has a choice between two enchants such as Rune of Swordshattering and Rune of the Stoneskin Gargoyle. If you haven't hit the 540 skill defense cap, take the gargoyle, no ifs, ands, or buts. Once you get past 540, there's some small amount of debate over which enchantment works best. 4% parry is a very nice chunk of avoidance. The 2% stamina on the gargoyle rune is still pretty nice, it works from all directions and even past 540 defense, you get some avoidance. If you feel like your stamina is a little low, or you want to unload some stamina for threat on your armor, you can use Rune of the Stoneskin Gargoyle to pick up some of the slack. Otherwise, that 4% parry will probably prove superior if you can keep your enemies in front of you.
   The second one is Head. For your head, DPS will want to pick up the Arcanum of Torment from the Knights of the Ebon Blade. For Tanking, you'll need revered Argent Crusade reputation for the Arcanum of the Stalwart Protector. It's a nice and straightforward choice, which is always cool.
   The third one is Shoulders. Like the head, there is another straightforward choice. Depending on your role, grind Sons of Hodir reputation and at honored you can grab the Lesser Inscriptions of the Axe or the Pinnacle. At exalted, you can grab the Greater versions. It is no doubt that you can also level inscription and skip the whole mess altogether, but otherwise, it's definitely worth the grind.