When should I use 'por' or 'para'?

There are quite a few scenarios in which 'por/para' required. This is a common use for 'por/para':
'Para' is used when you want to say 'in order to' (to express the purpose of doing something).For example, "Esta noche, voy a estudiar duro para obtener buenas notas" (Tonight, I am going to study hard IN ORDER TO get good grades).
On the other hand, 'por' is used when you want to say something happened 'because of' something (used to express a reason why). For example, "Por culpa del profesor, no saqué buenas notas este año" (BECAUSE OF the fault of the teacher, I didn't get good grades this year).