I don't think memorizing vocabulary is quite as important as learning sentence structure and how words relate to each other in a sentence. If you know how the word is used in a sentence you can use the words you do know to clarify the meaning of the word you don't understand.
I personally find that repetition and association helps most with the actual memorization for myself.
I do not think it is necessary to understand each word, rather, it is necessary to understand each phrase. Some words in a phrase can only be understood within the meaning of that phrase. Feel free to ask for examples.