One thing I would add, is: Make sure you are wearing correct gear for your class. That is do not wear any items that belong to other classes that contain stats that are completely useless to your class. While this may have no direct impact on what mistakes you do, but it does affect many other things. The affect of correct gear on how much dps you do is one obvious thing, but not the most important. The main thing is that having correct gear can affect what kind of attitude the the other players will have towards you.
If you show up in a group wearing wrong gear (not just sub-optimal but completely wrong gear that belongs to other classes and has stats that are completely useless to your class) then you already make a bad first impression on anyone who inspects you and even if they don't kick you right away, they will be convinced that you are an idiot before you even have chance to make any other mistakes and will only be looking for excuses to kick you out of the group.
Now if you at least show up wearing correct gear for your class, the other players might have slightly more respect towards you and will be more likely to forgive a few mistakes later on.
in your case make sure you are wearing gear with CUNNING and not willpower or something crazy.
if you have any orange gear (like your weapon)make sure you are upgrading it as you level and don't have the level 10 mods in it or something.
if you don't know what mods are or how to upgrade your weapon then read up on it or ask.