When people are bullied,i think there are two reason.
One is the case a victim has some causes such as their personality or their behavior.And the other is the case which victims are bullied with no special reason.(this is even worse.)
For the first reason,since I have never seen a serious bullying around me,i cannot really describe how victims' character are like,but I guess they are rather quiet and not outgoing,having some difficulties to socialize with others. Becasue I never heard people who has out going and cheerful parsonality is bullied.
I think when we face to situation there is no one who we know,such as a first day of school, it is very important how you will act like in front of those people. Because many of us judge whether they wanna be a friend with you  by a first impression.
For second reason, it can be said to the case when victim has no fault.
Assailant just wanna have someone to bullying even though there is no special reason.
I guess the trgger of this kind of bullying comes from assailants' personality ploblem.
Maybe he/she wasn't brought up in good home emvironment.

what can be done to decliese the number of this incidents?
hmm... it is difficult. One thing I came up with is that teacher should grasp how students' relationshiops are in the classroom. And should always concern students.Because recently, there are many teacher that take their eyes off from the fact that bullying is going on there. So that thay might help out  who are having trouble with frriendship.