Shoujo Manga's target market are female audience. Story focuses on strong human and romantic relationships and emotions.
And as a long time reader of shoujo manga, there are lots of similarities in one manga to another.
Here are list of the common character, event, etc in a shoujo manga (I'm still a fan):
1. FIRST DAY OF SCHOOL ENCOUNTER
= Main protagonist (usually a girl) late in the first day of school and hurriedly running down the streets. Then bumps into a stranger,got irritated and turned out to be her classmate (worst=seatmate)