If you mean that you are skipping grades then I would try and make sure to have everything ready and organized. Also alot of Jr. might not see you on their level even if you are so I also recommened trying out for diffrent sports and clubs, that way you also make friends all around your school cause even though Juniors accept some young peaple into their groups, they may or may not accept you with them. Good luck :)
Make good grades and make friends. That's all high school requires.