I know what you mean about cliques - they are everywhere from families to work to hobby groups and church. Since I have moved a lot, and have had to become part of the group over and over, I have a little advice. Remember who you are and what you have to offer- they do not know, so you must be strong in knowing your own worth. Almost any group will welcome someone who is willing to put in their share of the work, according to her own skills.
Everyone's natural inclination is to talk to those we know first - it's just plain easier. Find a friendly face and make an effort to visit one on one. Do this with more than one person to start making a network of acquaintences. The more often you go, the more familiar you will be and the "stranger effect" will be lessened.
Our Guild which is a BIGGIE (180 members or so) has a new member tea, which helps orient the newbies. I appreciated this because I had never belonged to a guild, and had no clue about most of the activities or even the quilting "lingo." It also offers classes which give you a chance to learn something new and be in a smaller group setting. It also has smaller groups within the guild called Bees. These smaller groups are easier to become personalized in and get to know others - we have a group that does charity work, others who just get together to do their own projects at the same time, one that does applique in particular, so there is a great variety of ways a bee can be structured. Our guild has a secret sister option, which is another way of getting to know a single person in a fun way, and over time adds up.
It does take a group committment to welcome new members, and it does take desire and effort on the part of the individual to belong. And ignore the snobs. Life is too short!