There are a lot of books available in the market for this purpose.Recommending a specific one won't be enough.Preparation and hard work is the best policy though but it would be a lot easier if you've already got a moderate grip on these subjects.The questions asked by the paper setter are usually not so difficult.
If you think that you're weak in a specific subject,start preparing right now for this and try to shift your focus on a single subject only for a definite period of time.