Hello,

The best way to improve your English is to read regularly. And as you are preparing for cat you must have a good reading speed to cope up with the duration of paper. The best thing to read is a newspaper. Because it has variety and knowledge gained from it can also help you in exams. The best newspapers are The Hindu, Mind, Indian Express. Try to read them as fast as possible. And if you do not understand that word first look for word meaning then go for full sentence meaning so you can understand the use of that word. In this way you can also improve your vocabulary. 

Just try to read different books that interests you. And don't feel afraid to speak in English. Try to speak english wherever possible.

Hope it helps.