Starting a mini series of posts that's going to focus around what to do when a hunter first hits 80. Seems like I've seen way too many "fresh 80s" who look and act as if they arrived in a foreign country. Althought this is targetted towards hunters, it applies to all classes.
Rule #1 -> Know your stats. The first stat you should focus on as a hunter at 80 is not agility, but hit rating. Why? Hit rating determines weather or not you'll hold up in a raid environment, heroic instances, or even PvPing. If you take 3/3 focused aimed (highly recommended) you only need a hit rating of 164 (or 163.90).
Next is agility. Depending on your spec you'll want to balance this with AP. In general the rule of thumb is 1 agi for every 2 rap. Even though 1 agi = 1 rap, agi gives you crit and armor as well.
AP is next. AP is how hard you hit for base damage. Almost every attack uses a formula that adds a coefficient to AP.
Crit chance comes after AP. Obviously the more crit rating you have the more often you'll crit, but without having a good amount of AP you'll be critting like a noodle.
Stam is also very important. A dead hunter = 0 dps.
Int provides mana. Mana is good. Don't give up any of the above stats for int though.
Rule #2-> Know your user interface. Whatever type of UI you use, default or custom, learn it and love it. Place your buttons in spots on the bar that MAKE SENSE. I like to place the spells on my main bar in order of priority. I.E Killshot, Explosive shot, serpent sting, multi shot, etc. Keep your UI clean and accessible.
Rule #3-> Learn about fights. Nobody likes a person who comes into a fight and either A) Doesn't know the fight or B) Expects the raid leader to explain everything. Remeber: A good raider is one who likes clarification not total explinations.