If you wish to be a BAT member, act as if you were one. Try and mod some people's maps, offering constructive advice and suggestions. Above all, be sure you like doing this for long periods of time.
Also, you probably have to have an adequate command of written English.
Even though I've long since retired from osu!, I'll always think of my time here fondly. If by chance you happen to notice this signature on some old forum thread, thanks for stopping by and I hope you're having a great day!