not sure what exam board you're on but when i was in gcse i did AQA, their specification for the course on their website had a list of vocab which would come up on the exam and i just learnt the meaning of as many words as i possibly could.
i guess if your exam is tomorrow then the best thing that you can possibly do is just learn topic specific vocab such as animals, environment, buildings, food, jobs etc. hope that helps! some key things that might help is learning negatives like ne ___ que, ne ___ pas, ne ____ plus, ne ____ jamais, or words like mais (but) and cependant (however), as sometimes the examiners will be sneaky and try to trick you by using these, i remember in my gcse mocks these are the things that caught most of my class mates out.