The direct object and indirect object, along with the subject and predicate, form the fundamental structure of a sentence. To distinguish the direct object from the indirect object in English, we simply identify which word is associated with the predicate without any intervening preposition. The word that is directly associated with the verb is the direct object; the word that is less directly associated, separated by a preposition, is the indirect object.
In Greek, this clue does not exist, because the indirect object does not take a preposition, as it does an English. The following test will work on both Greek and English for identifying the direct and indirect object.
To identify the direct object, ask the question "Whom?" or "What?" To identify the indirect object, ask the question "To whom? or "For whom?" or "To what?" or "For what?"