Hello,
IIT JAM 2019 will be conducted on February 10, 2019. To prepare well for the exam, primarily, you should check the detailed syllabus and exam pattern.
Referring the right books is important. 
Prepare a proper time table to schedule your preparation.
Devote time equally for all the topics and sub topics and try to complete the syllabus in time so that you have time for revision.
You should refer to previous year question papers to know about the types of questions asked in the exam and give mock tests after completing the syllabus to analyse your preparation.
With sincere efforts, dedication and determination, you can score well in the exam.
Also, you can go through the link below-

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

Good Luck!