*A few weeks ago, I had IELTS test and found the best book ,which improved my skills in Reading and Writing, "Check Your Vocabulary For IELTS". This books will build your vocabulary in simple way.... Believe me, it's the best one..
*If you want to do more practice like a real test , try to get this book " Cambridge IELTS 6", its useful.
*you should learn about writing structures, coz, each topic in the writing test has own struture as well as try to write essay as much as possible.