1) You have to remember that this is a stepping stone. Do not get overly addicted. This is the double edged sword. If you can avoid addiction, this will be a boon, if not, it will only hurt you. Don't forget that this is a stepping stone.
2) Join a non-top tier guild. You're here to learn how to overcome social anxiety, not to be the best damn xxx slayer.
3) Allocate a maximum amount of hours per day and per week you will play and a minimum amount of hours you will play with others while doing so. Do not let this simply turn into a game; it's purpose is to reduce social anxiety and have fun doing it.
4) If there are people in the guild who are local (let's say within 100 miles). Go and meet up with them. You will have an instant bond and conversation will flow much easier.
5) Just to reiterate the first point - this is a stepping stone.
Best of luck.