Write about one of your hobbies.

Pick a hobby which you're widely able to talk about and expand - likely something you're actually interested in as this makes it easier but if the vocabulary is complex (e.g. you have a hobby for rock collecting and don't know all the names of rocks) then feel free to pick something more simple.
Begin with a brief introduction to your hobby - what is it, how long have you done it for, how often do you do it, where, with who. Now try and expand - why do you like it? What is the worst part about it?
It's also important to develop your tenses in a GCSE answer so go back to when you did this hobby last weekend and tell a brief anecdote e.g. 'Je suis allé(e) à la piscine avec mon amie pour nager ensemble; je l'aimais bien parce qu'elle m'a fait rit.'
Now go to the future - talk about when you're next going to do it and, as an extension, whether you would like to do it as a career/in the future.
Read back over your answer very carefully checking all tenses, agreements and making sure your sentences are short and clear!