see dont think about taking year drops at your first choice, if you are in 12 also keeps preparing for 10+2 board exam and jee mains preparation. its true that jee advanced question level is higher than jee main level , but I would suggest you to give your best shot this year. then if your 10+2 score is good and you get the number 75% marks in pcm (general/obc category) in 10+2 course which is the cutoff for iits, nits and gftis. the marks criteria is 65% for sc/st. if you get achieve the good marks and also get good score in jee main , and you are really confidence about that you will get sure success in jee advance next year then you may opt for taking drop. keep it in mind that if you pass 10+2 course in 2020, then you can attempt jee advance in 2020 and 2021.