Did some script writing years ago as part of a similar project. Personally i would advise not going too crazy on the story but try and think of a situation that would make a good scene (assuming you are only writing a scene) first. You can fit the story after. I would also suggest you try and do something that has perhaps happened to you or a friend or something that is relevenat to your life/social enviroment. Then try and think through how you would react as each of the charecters. For example, say it was a scene about a kid who got caught shoplifting and you are doing the the Mum arriving at the police station and talking to the kid. What are they feeling? maybe also a scene with just two charecters would be easier anyway and you can really focus on the dialogue between the two. Yoiu will also be able to allude to other pieces of the story. In my example you could explore with the kid why they did it, what is going on at home, what's happening with Mum etc. Final piece of advice owuld be to steer away from comedy - it is easy to act but hard to write and it will be hard to get a sense of the story. Hope this has helped. Good luck!