Hey Mehak.

For preparation of DU LLB entrance exam for admission in 3 year LLB coursw You can use any all inclusive guide like Universal's guide to LLB and CLAT or Singal'a guide. Both these guides  includes basics and practice questions for the topics of DU LLB. UNIVERAL guide is used also for various other entrances. The Singals guide is also considered good for DU LLB. You can use any of these. Other than that you can refer to previous year question papers  for a better guidance. For current affairs and verbal section the Hindu is considered as the best newspaper. You can use Word power made easy- Norman lewis for vocabulary. 

Best of luck!