One common element is the element of secrecy. Teenagers often keep their feelings and these special moments private at first. For example, they might share a kiss in a hidden corner at a school event. Another element is the role of friends. Sometimes, a teen's friends play a part in getting them closer to the person they like, like inviting both to the same party. Also, the setting usually has some kind of significance. It could be under a tree where they often meet to talk, or in a place that has special memories for them, like a park bench where they first really connected.
Well, in many romantic teenage first kiss stories, there's the aspect of discovery. Teens are just starting to figure out their feelings for the opposite sex or for someone in particular. So, the first kiss is like a big discovery of a new world of emotions. Also, music or a special event can be a common element. For instance, at a prom or a concert, the atmosphere is charged with excitement. And there's usually a lot of blushing involved. After the kiss, both teens might blush like crazy because they're not used to such an intimate moment yet.