Hey.

If you are not attending any coaching for biology, you can refer any of  the following books along with being thorough with the NCERTS.

NCERT Biology Class XI and Class XII textbooks

 Biology Vol 1 and Vol 2 by Trueman

 Objective Biology by Dinesh

 Objective Botany by Ansari  

Pradeep Guide on Biology  

GR Bathla publications for Biology  

Do not neglect any topics. Lay more emphasis on the important chapters. Divide your syllabus and make a schedule accordingly. Make sure you stick to it to. Try to make notes while studying, and make it a point to revise these notes. Other than that, you can practice various sample papers and previous year papers.

Best of luck!