If you get the feeling when you wake up in the morning and smile because you know you have something to look forward too. If you get excited to see them everyday, when you can be yourself and not worry about being anyone else. If you trust him/her. I hope it helps.
look at the person u like if u are a boy look at your pants a.) is it hard .if yes then you are in love if no then you are not in love if you are a girl you will find yourself speaking faster, butterflies in stomache