I want to score 300 in jee mains.I have 1 year to left is it possible if i start from now and practice thoroughly

http://www.askiitians.com/iit-jee/main/preparation-tips/

The above link will give you a brief guidance about the preparation tips for JEE Mains.Although the site needs to be updated for 2017, please note that the basic approach towards the examination remains the same.