Hello,

• You must begin with covering the entire syllabus of JAM Mathematics.
• Solve, practice and analyze as mant sample papers or previous years' JAM question papers as possible. These will make you familiar with the difficulty level of the paper, exam pattern and marking scheme. 
• Get all your doubts cleared by teachers ot friends as and when they arise. Having clear concepts is very important.

You can visit the link below to know about books and other important tips for IIT JAM preparation:

https://university.careers360.com/articles/how-prepare-jam-mathematics

All the best!

Here are soem of the books you can prefer for IIT Jam MAthematics give below:

Mathematical Analysis by S.C. Malik, Mathematical Analysis by Apostol, Principle of Mathematical Analysis by Rudi are best to cover the topic Functions of One and Two Real Variables; Real Analysis by H. L. Royden for the topic Real Analysis; Geometry & Vectors by Vasishtha and Calculus by Thomas & Finny for Vector Calculus. 

You can also prefer the below given article for the further information.

IIT JAM Mathematics Preparation

Good Luck!