Best way to 'handle' what would appear to be a belligerent 11 year old girl?

From my ex wife I know when my daughter was going through the 11 YO stage of throwing a temper tantrum every time she wanted to get her own way , It took me five times to get her shed of that habit , I placed her in her room on a long time out and said Let me know when your done so we can talk like human beings , about every 30 minutes I would open her door and say " Are we done yet " Then close the door if her tantrum went on , in time there were no further Tantrums .