Hi, The BHU LLB entrance has the following sections:

• English Comprehension
• General Awareness and Current Affairs
• Aptitude and Mental Ability
• Common Legal Knowledge

For preparation you can first refer to previous year sample papers and go through the kind of questions come in the exam. Also the above sections are common to most of the law entrances so there is nothinh new to add. Give sectional and full length mocks to practice well and sove complex questions. 

All the best.