DU JAT has the section Quantitative Ability, Reasoning and Analytical Ability, General English, Business and General Awareness.

You can follow below section wise preparation tips

Quantitative Ability

In this secton the questions generally asked from 11th and 12th Mathematics syllabus and some questions from 10th grade. Solve as many mock test as you can. You can prefer RD Sharma book.

Reasoning and Analytical Ability

In this section questions will be related to bar graph and chart etc. Any data interpretation book could be helpful for this section.

Verbal Ability: To prepare this section, Read newspaper and Novels you You can also solve previous years paper.

Business and General Awareness

To prepare this section, I would suggest to read newspaper daily, You are also advised to remember national prize winners of current and previous years.

Good Luck!