Zones of interest
At the early 40's, you should be wrapping up quests in Dustwallow Marsh and Stranglethorn Vale. STV's considered one of the worse places to level (on a PvP server) due to players roaming around looking for low level characters like you to take out. Be on your guard or see if you can enlist the assistance of higher level guildies. Alternatively, you can always level early in the morning or late at night when the zone isn't as populated.
Hope over to Theramore and catch a gryphon to Tanaris. This desert wasteland will boast gankers as well. You will find the goblins to be most hospitable while you spend your time out there taking out pirates. Don't forget about the quest hub due straight east from Gadgetzan.
When you're finished, get ready for the long trek towards Feralas. You can either approach it from the north via Desolace of from the east via Thousand Needles. The drawback to coming from the east is that you might run into a minor Alliance camp or a larger Horde stronghold. Maneuver around them accordingly. For the Alliance, the major quest hub is located to the west off the coast of Feralas and there is a boat that will ferry you there (Feathermoon Stronghold).
Once you're done, consider taking the boat from Theramore back to the Eastern Kingdoms. I don't think you've reached the level where you can comfortably start Un'Goro. Start working your way up towards Southshore and head over behind Durnholde Keep. You'll find a path leading north and you'll eventually run into Aerie Peak! Check out Burning Steppes and Searing Gorge and by now you ought to be pushing level 50.
Un'Goro Crater: Ready for one of the most loaded video game pop culture reference zones ever? Be sure to bring yourself a Mithril Casing before you fly down here!
Azshara awaits! You'll run into the quest area and flight path as you run in from Ashenvale. Memory's a bit rusty on this one but I do think there's a set of quests you can do towards the north once you've exhausted this area. Otherwise, there isn't much to do here. If you see a big giant dragon named Azuregos, be sure to run in the opposite direction really fast.
Make your way towards Felwood and the Emerald Sanctuary. Make friends with the Furbolgs and be sure to get the second flight path on the north end of the zone. Head on through the tunnel while stopping briefly at Moonglade. When you get the path there, carry on towards Winterspring and Everlook. You may need to alternate between these areas, Silithus, Western and Eastern Plaguelands. That should be more than enough to tip you over to level 58 if not 60.
Now you can set foot through the Dark Portal in the Blasted Lands.
Scarlet Monastary: If I were to hazard a guess, Scarlet Monastary would be the highest run instance for mid level players. It drops decent loot and doesn't take much time to do at all. Having 70's to go with you makes the run all that much faster. Scarlet Monastary actually consists of 4 different wings you can do: Graveyard, Library, Armory, Cathedral. The SM Graveyard doesn't have a whole lot for you to do in terms of bosses. Most players typically run Cathedral the most (judging from trade chat requests, at least).
Zul'Farrak: Welcome to Troll town! After killing several million basilisks and fighting a massive gauntlet and summoning a really large monster, you'll come out with some phatter loots and hopefully another level of experience out of the way.
Temple of Atal'Hakkar: Also known as Sunken Temple. Each class has their own level 50 quest to do here that involves feathers.
Dire Maul: Sadly, I rarely see players run this particular set of instances anymore. I believe it consists of a north, west, and east wing respectively. Ogres have made their home here. Watch out for the arena in the middle of the area.
Blackrock Depths: Personally, I'd avoid this area. But that's just me. Still, it's another option for you and Molten Core attunements are inside as well as Onyxia (for Alliance anyway).
Spells and abilities
I won't bother detailing some of the Priest racials as they will be phased out and removed. Most of the new spells you learn will be from talents. Everything else will be new ranks of the old and I won't bother listing those either.
Power Infusion: The earliest level you can get this talent is at level 40. It allows you (or anyone else) to cast spells faster and at a reduced mana cost. Use it often as it only has a 2 minute cooldown and lasts 8 seconds. Obtainable at level 40.
Pain Suppression: Reduces damage taken by a friendly player by 40% and drops their threat instantly. Not only that, it increases resistance to dispels by 65%. Like Power Infusion, it can be used every 2 minutes. Useful in a pinch if you accidentally over pull or come across something larger than life. Obtainable at level 50.
Lightwell: The effectiveness of Lightwell is dependant on the abilities of other players to take advantage of them. When they right click on it, they gain a buff that restores health over a period of time. Obtainable at level 40.
Circle of Healing: This is an AoE heal that heals your target and your targets party provided they're within a certain range. Virtually useless at the lower levels. Prayer of Healing will perform what you need. Very valuable when you arrive at the upper levels of end game raiding. Obtainable at level 50.
Vampiric Embrace: Applies a debuff on the target. Anytime you deal shadow damage, your party is healed for 15% of any shadow damage that you deal. Picking up Improved Vampiric Embrace will double the amount healed to 30%. Obtainable at level 30.
Shadowform: Ready to give in to the dark side? With this, you'll turn into a more sinister version of yourself increase your damage output by 15% and reduces physical damage done by the same amount. Drawback? You can't cast Holy spells so healing is virtually out of the question. Well, no, Vampiric Embrace is an exception.
Vampiric Touch: Deals a minor amount of damage to the target. More importantly, it restores mana equal to 5% of any Shadow spell damage you dish out. Very handy.
Looking for tips and tricks for leveling up your mains or alts? Check out our page of WoW Insider Class Leveling Guides!