Pick up weapons will cause a lot of damage
During your training, you should be able to pick aion kinah up weapons that will cause a lot of damage to a mob you are fighting and you should practice with it a lot to ensure that you know how to handle yourself when it comes to being in an instance.
When you are invited to be in a group, and you have the time to run the instance, you should go. It doesn't matter if you have run that particular instance before or not, the more experience that you have with any instance, the better you can do overall in the game.
If you aren't familiar with that particular instance, ask your friends or guild members who have been there for any tips or advice that they can give you. You can also check with some of the World of Warcraft websites that show quest information and give advice on different areas of the game.
Meet with your party and greet them all warmly, after all, they will be covering your behind while you are in the middle of the mobs. Ask politely for any buffs that will help you, or anything else that your group members can do or provide (such as potions or enchantments) that will allow you to be a better tank.