Book club is actually an excellent way to practice socializing for people with social anxiety, because the onus of conversation is on someone else (the discussion leader), you can prepare your thoughts ahead of time, and everyone has a common interest and shared expectations. Each club is different, but in mine we don't force anyone to speak if they don't want to -- you can show up and just listen for 90 minutes without saying anything, if you want. You're going to have a great time!