In my Chinese textbook, 谦虚好学 is used, and 虚心求教 is used as well. They both mean modest, so when should I use each one?
謙虛好學 means "modest and eager to learn", usually used by teachers to praise the students. When you use it on yourself, praising yourself as "好學", you are not "謙虛" anymore.
虛心求教 means "seeking help/solution/knowledge in a modest manner/attitude"; in addition, "虛心" also implies that you are ready to un-learn some of your prior knowledge. You can use it on yourself but you must be very careful.
虚心 and 谦虚, in fact they are almost the same. you should always find that, in Chinese, there are always many words saying even exactly the same meaning, which makes Chinese very flexible for using.
Basically, 谦虚好学 is used to praise others, don't use it on yourself. 虚心求教 just the opposite.