I am of the opinion that the best thing a hunter can do to improve themselves is read. Hunters are complex and there's a ton of math behind our damage. Additionally, a lot of our skills have changed, and as a long time hunter I find myself forgetting how skill's I've had forever work.
Arcane shot and Distracting Shot are two great examples of this. When I started huntering Arcane Shot was more or less what it is now, but as I'm sure any of you Burning Crusade Vets remember, for a time it had a dispel slapped on it. It was never a very popular change, and I myself often forgot it had been added. They've since moved this effect to Tranquilizing Shot, admittedly a more appropriate place for it, but now I find myself thinking it's still attached to Arcane Shot.
Distracting Shot is another shot that has had it's mechanic changed. Once upon a time it "generated a large amount of threat". Now it acts more like a taunt. This has had the side effect of many old school hunters, like me, to use this shot in conjunction with Misdirect, which used to work. Since Distracting Shot is now a taunt and generates no threat the hunter pulls the mob they were indenting to Misdirect. Yes, I have done this. /bonk
So what's my point? Hunters need to read up on the current updates to the hunter class, as well as know the old stuff that's been around forever. To help you out here are some articles that hunters new and old alike may find useful.
Mend Pet's Ten Do's and Don't's of Misdirection.
This article is geared more toward the newbie hunter, but even us old hats can find something new here. I personally will be trying the mouse-over macro, as the macro I currently use requires me to select the focus target to set it.
Ghostcrawler's most recent comments on the hunter class
If you are not aware, Ghostcrawler is kind of like Blizzard's mouth piece on the forums. He discusses mechanics, changes and community concerns. Love him or hate him, he's the guy in the know, and you should read what he has to say.
Duel Specs in Ulduar
Drotara of QQ pwn more has some thoughts on utilizing Duel Specs in Ulduar. It's worth the read even if you don't use duel specs for raiding.
Some Advice on How to spot an Upgrade
Wow.com's Eddie Carrington has posted his second edition of Scattered Shots. This article focuses on Item Level and how to best judge an item. What's Item Level you ask? A surprising number of players don't know, so if you're not sure what this is, this article is a must read!
So keep up on your reading! If you're not sure where to start, check out wow.com, they often have the most up to date information on any class and they always try to provide it in a timely fashion.