The top Universities  of three years law programme is Faculty of Law, Delhi University, Faculty of Law Banaras Hindu University, Punjab University which you can prefer. The colleges have its own entrance exam. The syllabus is almost same for the three years law programme of the colleges.

The preparation tips you can follow given below:

Plan a strategy: It is a must to schedule a study-plan. An intensive preparation strategy is needed which includes as many as 6 hours of regular studies to crack DU LLB entrance exam. you must study at least two subjects every day and must practice at least one vocabulary / English and one reasoning exercise daily.
There is no defined syllabus for GK and current affairs in this exam. You can focus on important awards each year  sports, science, literature and arts, Physical geography, science and environment, Important happenings in the area of the Indian Constitution or Justice system
Mocks form an important part of the exam preparation. Look for a good online mock test series, and aim to write at least 6-8 mock tests before the actual exam. Reproduce the exam conditions as much as possible.

You can prefer the material of Delhi Law Academy for the preparation.

Good Luck!