I never really played demonology, not my playstyle, but there are some basic things that should help you out.
Watch your aggro, just like you don't want to pull a mob off your Felguard, you don't want to pull off a tank. The difference is while your felguard has a somewhat steady aggro, tanks can vary wildly. You might find some you just can't pull aggro off and then some a few dot ticks will pull aggro off. Always target the tanks target if they aren't using marks and go easy on the first few pulls to see what kind of tank you have.
Don't let your felguard intercept as a tank usually needs to take damage in order to build threat, a stunned mob doesn't attack and can thus hurt the tanks aggro building. Save intercept for certain situations like a mob is on the healer. The same goes for anguish, keep it off and only use it for special situations.
If there is any crowd control turn cleave off, however most people don't bother with cc any more, makes me sad.
If there is another caster in your group, except boomkin, switch from CoA to CoE, and depending on what melee classes you have you could also switch to CoW to boost their damage.
For a rotation, use immolate and incinerate, corruption on fights that last a little while longer. Dunno about Outlands but most tanks at higher levels prefer to aoe tanks, thus your best bet would be to cast rain of fire or seed of corruption, just make sure the tank has aggro on everyone first.
Ask questions when in the group, if you've never been there ask if there is anything you need to know about a boss. Despite the I hate pugs mentality people seem to have, I find there are always people that are friendly enough to help a person out. However, you'll also run into the 1-wipe and the healer/tank leaves situation as well, take it with a grain of salt. Leveling dungeons are where your supposed to learn how to handle yourself in a group, so when you get to end game you don't "really suck/get yelled at/die often/not contribute". Leaving because of a wipe teaches you nothing but impatience.