1）用to的话,表示做某事给某人,或者是某人是动作的承受者.如I bought a bag to my mother.我买了一个包给我母亲.原本并没有这个打算.
2）用for的话,表示为了某人而做某事,如I bought a bag for my mother.
我为我母亲买了一个包.表明了目的
有些时候,两者的意义有较大区别,例如,
Going to bed early and Getting up early is good for you.
早起早睡对你有好处.
Susan is good to me.
苏珊对我很好.（此处good相当于nice,态度好）