Just wear an avatar YOU find cute/cool and then chat. Its that simple. You don't gotta act cute unless you want to try to make people cuddle/erp/etc. you. Personally, I act cute because I like seeing anime tiddies bounce in the mirror.
People aren't going to orbit and constantly give you attention you unless you make yourself the center of attention, so don't get sad if people aren't constantly chatting you up. Just get in the group and chill and contribute whatever feels good to you.