“我不擅长于…”应该说：

I am not be good at.

领导人应该擅长制定规则。

They should be good at making rules.

部分拉拉擅长开门开锁。

Some can be good at opening doors and latches.

非常喜欢长笛，还擅长古筝演奏。

Very like flute , and to be good at zither.

电脑操作熟练，擅长数据管理。

Computer operates adroitness , be good at data management.