The main group that I am part of is called Obscurus Crusade and they focus mostly on Warhammer 40K costuming. This is a great group of people that i had the pleasure of meeting a good many of them at Dragon*Con 2011. This group is a good group for people that are just starting out or if your an old pro. I came to the Obscurus Crusade with very little costuming knowledge and was a little afraid to as some of the Newbie questions, so I stalked the forums for a little while and after seeing the kinda of help they were giving people I started posting and asking questions. The help and also motivation i received from these guys was essential in finishing my Inquisitor costume.
The other costuming group I am part of is K.A.G (Klingon Assault Group). This group focuses mostly on costuming for well....Klingons. They are also an activity group and also do a lot of charity work. This group is also full of lots of knowledge and craftsmen. They are very welcoming to new members and love to help get new members "ridged up'd" as they like to say.
Now just talking groups in general there are good and bad things that come with being part of a group, The good thing is that you are able to make a lot of new friends and the knowledge. The bad thing is that there can be a lot of Drama so be warned. Not all groups will be drama filled but some are. I know that some people do great with groups and some don't so it's your own preference. Well ladies and gents I'm going to close up this article with one piece of personal advice from yours truly, "do what feels right for you, if you like going solo then by all means stay solo. If you like having a group of people to ask advice from then please find a great group."
Have a great Evening everyone