Alludra the Mannerly Mage here helping you be a player who gets invited to all the groups!
Something I have noticed is a lot of impatience some gamers have with the learning curve. While it's true that most low level players are alts of an established player, this isn't the case for everyone. Sometimes you will run into players who are running content for the first time and don't know all the tips and tricks established players take for granted. Heck, there is even information that a lot of end game players aren't aware of!
My favorite pet peeve in this instance is how players treat new tanks. As if there isn't a shortage of this class, I constantly see bragging from players who should know better about how they pull aggro from the tank for entire runs.
Some people treat this as if they are doing the new tank a favor, but they are ignoring the frustration they may be causing the rest of the group by 'taking matters into their own hands.' And when they die? Well you can bet it's not their fault!
Look guys, we know that leveling is a bit boring if you have been there, but let's actually try to help new players instead of being some jerk that makes everyone's instance less fun. Something to ponder when you are looking for another tank to round out your raid or instance.