Even when you do get a group together via the Group Finder (and not the "old-fashioned" way), communication is always going to help your group be successful. Now that the Group Finder is out, lots of players may be trying out Flashpoints or Operations that they haven't tried before.
If you've never done the content before, it helps to speak up! Let your group know with something as simple as, "Hey, I've never beaten this Flashpoint before - can someone explain the bosses/mechanics to me?" Generally, someone else in the group will be able to offer you a brief explanation. Letting people know that you've never been but are willing to pay attention and learn is always much better than making a mistake!
If you have done the content before, you can help by stepping up to explain. Some people may be afraid of how a group will react if they're new, so take the lead and help! If someone seems to be having trouble (or if they're doing something wrong) and you can offer tips, do it! Remember, everyone has to do something for the first time once, and it doesn't help to get upset with people right away - give people a chance and some explanation and encouragement.
Good communication is definitely a key to success, so speak up!
There are many people out there that do not listen period. And frankly Im getting tired of babysitting for players who either don't have a clue as to what they are doing or are wearing the worst gear out there and expecting to be carried through an instance. For the love of all that is holy at least put in a gear check for certain hms so people dont get stuck with complete imbeciles who don't listen and are not prepared for a flash point. I swear if I get put into a HM LI with another tank that has 13k hps and doesnt even have implants or an earpiece I am going to scream.