Guardian is a cheesefest once you get Eko. Follow the talent guide on wowhead, it's actually decent.
Moonfire, keep dot active.
Thrash to 3 stacks, keep dot active.
Mangle on cooldown.
Swipe when above actions on cooldown.
Ironfur, keep at least 1 stack up.
Maul when Incarnation is up (hits three targets), or you don't need to use defensives, or you're spitting out rage and everything is on cooldown.
Defensive Cooldowns:
Barkskin: 30s 20% dmg reduction for 12s, 60s cooldown, no rage cost
-I use pretty much on cooldown, but it can be stacked with other defensives
Survival Instincts: 2 charges, 3min recharge, 50% damage reduction for 6s, no rage cost
-Save for big hits.
Frenzied Regeneration: 2 charges, 24sec recharge, heal 50% damage taken in last 3sec
-Use after big hits if there is going to be a gap in damage, and you're rage capped with 2 stacks of Ironfur.
Incarnation: 15% armor for 15s, 3 min cooldown, reduces Taunt to 1.5s, Maul hits 3 targets
-Mostly a dps, add cooldown.
Stats: Armor>Stamina>Versatility>Mastery>=Haste>Crit>Agility
At a certain point, Haste becomes more effective, since you'll need more dps than defensives.
Trinkets: Armor boosting > all.
Smoldering Titanguard is amazing.
Tier 21 set bonus is pretty solid.
You can just roll your hands over the number keys and play guardian well enough for heroic, hilariously.