1- You can only join a group of you are either a Loner or a Rouge.
2- Ask Permission. You cannot join a group unless you have permission from the group leader, saying that he approves. If this is not done, then your request may be denied.
3- Members in Groups will keep their rank until they either die or, if they are exiled from the group. And one you leave you'll lose any special abilities or traits in which that group had.
4- You may only be in one Group at a time, this also counts for Alternative characters, one one character at a time in a group.
5- Some Groups will have special items and tokens as a symbol of the group, this could be anything from a ring to a sword. If this item is damaged, destroyed or lost, you will be kicked out of the group.
6- Groups can have a maximum of 10 Members. If all the spots are filled you'll either have to beat or kill a current member. Some may not approve of this but it proves your worth to the group. When you first start the group though, it can only have a maximum of 6 members, That is including NPC's. However if your group has a 5-Star Rogue in it, that can be increase to 8. If 2 of them, then its increased to 10 spots, but that is the limit.
Follow the rules!