So, today I begin the process of really learning how to play my favorite MMO again.  That is, I am beginning to study the game with the intent of playing at an above average level.  My end goal is to be a competent, competitive player when I do log on, even though that will be less frequently than the 19 year old college student with infinite time to play games.

I might never raid properly, on a schedule and at the higher levels, but I do intend to gear up and have fun with PVE instance play.

If anybody has returned to Warcraft after a long leave of absence, they would immediately be struck by the sheer amount of options that exist the moment they log in.  Here are some of the questions that I had right away:
Where am I?
How do I get back to Org?
How do I get to the panda island?
How should I set up my UI?
What addons are good now?
What is the best healer in the game now?
How should I level, and which character should I level first?
Should I run through the extensive quest line?
Should I run instances before I hit 90 (level cap)?
How should I spec my priest?
What spec should I use for questing?
As I approach 90, what do I do now?
What factions are out there and what do they offer?
Where do I find the daily quests, and which ones should I do?
Where do I start getting better gear?
What stats do I want on my gear?
How do I make gold now?
What professions should I work on first?
Is farmville useful or a pure waste of time?

So, that is what my first few hours of gameplay were like, although I managed to grind through a few mini quest lines on my shadow priest/disc priest.  I started doing some google searches and found some decent forum answers:
I just hit level 90! Now what? : wow
Level 90... Now what? - Forums - World of Warcraft

Here are some good things I've learned so far:

• Disc priests are still quite viable in MoP, which is the acronym for the newest expansion.  They are good in instances because they can DPS while they heal.  Other priest specific resources indicate that spirit is important for mana, and intellect is now only tied to spell power.  Good to know.
• At level 90, buy the flying ability for the panda area at the Shrine of 7 Stars.  It's called "Wisdom of the 4 Winds"
• Some of the factions in MoP include: Klaxxi, Golden Lotus, Shado-Pan, August Celestials, Angler, Tiller, Cloud Serpent, Shadow Pan Assault, and Kirin Tor Offensive.
• Valor points are used to buy pretty good gear.  You can only get 1000 Valor points each week.  If nothing else, make sure to get those 1000 Valor points every week.  You get them from heroics and dailies.
• Dailies yield reputation and Lesser charms of fortune.  Those are turned in at the Shrine for Mogu runes of fate.  Those allow you to roll an extra time in LFR and raids, helping you get better gear.
• Klaxxi have an item level (iLvl) 522 Epic neck at honored for 1250 Valor points.  This should take about 1 day of dailies after I have done the Dread Wastes quests.  Mobs yield amber shards.  Turn those in for "Lesser runes."
• Each faction has a badge at revered that gives 100% increase to rep gains for all characters on the account.
• Tiller dailies are all about planting and farming things.  They provide extra mats and stuff for my character or professions.
• Three primary options exist for PVE groups.  Random scenarios, 5 man heroics, and LFR (Looking for Raid).  LFR requires an average ilvl of 460 for the first set of bosses.
• Random scenarios queue quickly and have less people in the party; they are supposedly much faster.  Scenarios offer 450 and 463 blues, and sometimes 476 epics.  They give 40 Valor points for the first one done each day.

Right now I'm 89, about 2/3 the way to 90, on my priest.  Apparently, the real game starts at 90.