First you need to get comfortable moving your body to music. So start by listening to some music that you like at home and start dancing there.
Next step would be to go to some concert with loads of people where you are in the anonymity of the masses and dance there in the crowd.
Once you are comfortable doing that you should be easily able to do that at a bright festival.
If any of those steps seem too hard for you at first start doing this drunk and then reducing the amount of drunkeness at additional attempts.
