Well, it depend on how young you are and how long you have been in a relationship. If you two are dating and you and he have strong feelings for each other(usually you can tell by his actions if he...
if you both like each other...as soon as he leaves (goes to his next class, goes to his car, etc) call his name and tell him to come over where you are really fast. when he comes back, kiss him...
Its actually quite simple. 1.) She will probably be biting her lip. 2.) She will have her face close to yours. 3.) She will be looking into your eyes as much as possible. 4.) She will try to be alone...