Maths is really an easy subject if studied with upmost concentration. It is one of the most important subjects whenever competitive examinations are considered. To build a good basic of the competitive exams you need to study this subject deeply. Every concept should be crystal clear, which will help your higher classes.
According to me, R D Sharma is the best book for Maths. This book contains plenty of questions which will help you to increase your accuracy and will give you deep understanding of the topics. The pattern of the book is so similar with the board exam pattern which will help you to be familiar with the ongoing exam trends. First, you should study from NCERT and then only you should go for some additional reference books.