Cooldown stacking and burst is so important right now that Force of Nature will probably be too weak for many comps... especially dps/healer in 2v2.
... speaking as a force of nature fanboi.
To add to what Reflex said about calling targets:
Be sure to test the waters with the other players in the field. If you know you generally can't drop a holy paladin - you may opt to try to kill his partner first. However, if that doesn't look successful, *try* the paladin. He may be wearing PvE gear or be a bad player. I've lost against teams assuming a target wasn't viable, only to /facepalm in later match-ups when I discover that player is abnormally squishy.
So, perhaps a mish-mash of examples of how *I* think will help you in your endeavors.
Here's how I break down targets:
1) Identify classes that my team can kill easily.
2) Identify classes which are especially dangerous to my team.
3) Identify how classes can be shut-down... through CC, training, or LoS.
4) Identify if any classes are vulnerable to swaps and under what conditions.
The first priority is identifying threats. Some threats are so great, you must take care of them or lose.
For example, I've been running fire mage/boomkin. We've found that we just can't really kill warriors. It takes a coordinated burst attempt from both of us to drop them through 2nd wind. So in many warrior/xx matchups, we want to kill xx.
However, the warrior has such great control, mobility, and damage, we often CAN'T kill the warrior's partner while the warrior is attacking us.
So we start warrior, not intending to kill him. Fortunately for us, the warrior doesn't know this. The warrior often leads the charge, so we can get first strike on him before his partner has really entered the battle.
What generally happens is: We nearly kill the warrior - scaring him into playing defensive. While he is defensive, we now have an opening to swap to his partner and actually score our real kill target.
Many comps have instant un-healable damage that they apply in the beginning. If the other team has that capability and you don't, you need to stop it so you don't lose before you have a chance to win.
Another thing I like to do early in the game is apply pressure with the purpose of setting up a swap kill later. Healers are generally really difficult to kill if they are prepared for you... which means they are often vulnerable if they're un-prepared... they generally deal with surprises by using one of their outs. This may be pain suppression or bubble.
An example of how I often play this:
Against paladin healers, we really struggle to kill anyone the paladin is actively healing. I'm not sure of the paladin healing mechanics, but it is super hard to put any pressure on our kill target when the paladin is actively healing them.
If we're facing:
Demo Lock / Warrior / Paladin.
The demo lock can be killed after he uses his damage immunity move and his healing.
The warrior is incredibly difficult to kill, so we don't generally want to kill him.
The paladin becomes vulnerable after he uses his blessing of protection.
The warrior needs to be controlled or playing defensive in order to land kill attempts.
We need to swap targets, because the paladin is great at healing against a train.
As I mentioned before, the warrior is a real trouble spot for us - we can't really kill anyone unless we do something about him. We have two options: Open on him and get him to play defensive OR we can control him. Since we can line-of-sight much of the locks damage, we don't need to worry too much about putting DR on the warrior before he pops cooldowns. So we choose to pounce->clone the warrior, while the mage opens on either the lock or the paladin.
I prefer to open paladin. The paladin's defensive bubble is good for saving himself AND his partner. So if we go on the lock, we have 5 main defenses to get through. His shield, His healing, His trinket, His paladin's bubble, his paladin's trinket. If we go on the paladin, we have just 2 defenses to go through: His bubble and his trinket.
Attacking the paladin can force him to use his bubble and/or trinket. This takes 2 defenses from the lock as well.
On our next burst attempt, we'll go on the lock. This will force the lock to use his bubble and or healing.
On round 3, you have two vulnerable targets to kill.
Of course, their CC and offense will delay your kill attempts. If it's delayed too much, they'll start getting their cooldowns back - making it a losing process. So key to this is running control on the warrior, enabling us to get kill attempts on pally/lock, while mitigating as much of the locks damage as possible via LoS... so that we're not forced to retreat too often.
When I used to run feral/rogue.
Against healer/dps, we would sap the healer then open on the dps at range. If the healer trinketed the sap, we would smokebomb. We would cyclone after the smoke.
We sap, paladin trinkets, we smoke, he runs close, we clone, we win.
We sap, paladin bubbles, we smoke, he runs close, we clone, he trinkets, they win.
When you have a plan for managing or using up the other team's defenses, you need to know when things are going according to plan and when things are not. In the above example, as soon as the paladin bubbled the sap, we knew our kill attempt was over and it was time to play defensive - to hopefully get a 2nd attempt 1 minute later when our cooldowns were available again. Delaying that defensive play could cost us the game.
The last key factor is identifying how to shut down certain classes. Many caster dps really struggle to do damage while being trained by a melee. Many classes in general have very specific setups they need to do damage or take control of the fight. Awareness of these mechanics are important when you're choosing your target. You may want to play a strategy where you spend most of the fight shutting down an enemy player, in order to enable you to be in a position to make kill attempts later.
As you know, feral druids rely on Savage Roar in order to do damage and PS procs in order to give utility. Ferals generally do a 0 combo points Savage Roar in stealth before opening - then try to build 5 cps quickly in the pounce. If you can stop the combo point generation for 10 seconds, savage roar will fall off and the feral will have to restart his dps cycle. Early CC on ferals is extra effective in slowing down their dps. If someone on your team has an offensive dispel, they can dispel the feral's PS procs robbing them of instant utility. So against many feral teams, working to foil his CP generation early in order to give inertia to your own team can take pressure off of your offensive dispeller. The reduced pressure can allow them to remove the first PS proc the feral eventually gets... compounding the issue.
Frost mage damage revolves around frost bomb - which has a 10 second cooldown. Melee riding the mage can alternate kicks/stuns/cc's and defensive moves in order to negate the frost bomb damage. Mages are super difficult to score kills on for many comps, but they're a good filler target for when you're between kill attempts. Not only does it slow their damage, but not all mages are created equally and you may find that a bad mage will give you openings to kill him.
Shadow Priests need to get dots rolling (Vamp embrace) in order to trigger their instant cast burst damage. Training a priest early and keeping him from applying vamp embrace can take their damage out of the equation.
So I hope a little window into some of how I think about it, will get you going in your own matches. Good Luck