Idk if your a girl or boy so for Boy: work out more often, you will feel confident about your body, talk to girls that arnt popular, for example the ones that are nice to everyone, this will help you feel better about communicating with girls, get a hair style that looks good on you. One of the big things is have style, when you put effort into looking nice girls will notice. There's many guys at my school that aren't very attractive but on a non uniform day (I go to a school with uniform) the guy get a lot more attractive. If you go to a uniform school alter your uniform to make u stand out. Take risks when your not at school. So if your some where far from home, talk to girls "out of ur league" practice talking to them and if you get rejected, you learn. Girl: makeup. But not a lot, go on YouTube and look at tutorials. Try making your hair look different every day. To feel more comfortable to talking to guys talk to a seating partner or your friends guy friends.
Hope that helps :) I can try and give more if I knew your gender :$
If you are a guy work out or work at something you excel at even a little and become the best around. even if it is a stupid video game be the best that ever there was. make people laugh on websites like reddit and funny. be amazing in your own way
well if your a boy the best way to be confident in yourself is to boost urself up like energy drinks or soda or get some new shoes make friends or hang around people who are confident in themselves and what they wear and do or people who have so much spirit and hyper join a sport you have team mates the encourage you maybe what you need to get confidence in yourself you could try a new hair cut or style that will really caught peoples eye into saying hey you look nice witch will give u confidence if your a girl you simple try doing stuff that makes you happy like join a activity thats working with a team or try new styles or new things that will caught peoples eye or attention who knows some people may really like it and say hey you look good or something