What should i write?

Today i write a essay the title is vehicle. Friends, vehicle. What i can write about it. I think it about one hour i also can't come out anything. In MUET exam, writing is the worst part for me, and get the lower score in this part.I'm try to improve my grammar my vocabulary but still no effect for my writing. What should i do about it? Any idea let me improve my writing skill? Friends give some idea and i will appreciate it.