How should I manage to crack iit from October along with boards if I m just an average student.

@ abhi 
it will be little bit difficult to manage time as boards are ahead and also after that 1 week to your jee main . 
so, what u need to do is now revise 11^th syllabus for 3 days in a week and rest 3 days to class 12^th , ths u have to continue upto december 2^nd week , and once your school starts preboard , after that no 11^th , only 12^th u have to focus , beacuse acc to me , boards is somewhat imp for u now , beacuse u can take drop and attend jee next year , but board will not come again . 
and u need to be in top 75 percentile for jee advanced . 
but be carefull – during this time , dnt forget the concept that u already revised , otherwise it will make u trouble in boards , b oard demands everything to be explained . 
AND IN these times , if possible try to practice the last 5 years ques paper of jee , 
ALL THE BEST ..