I think that you can memorize many words but the most important is if you know when and how to use it. When you memorize many words you tend to forget it and this is because we don't use all that we learn, we use just the same popular words everyday.

Flashcards. http://www.memrise.com/course/6792/cet-4/ I found an English course based in Mandarin on my favorite flashcard website, Memrise. Unfortunately, there aren't a lot of Mandarin-based courses on Memrise yet (it's a pretty new site), so you'll likely have to look for another site yourself. But yeah. Flashcards are the best way to really quickly learn new words. Of course, USING words properly is best done by speaking to natives, so when you have a large enough vocabulary (I'd say at least 1000 words so you're not completely lost), use this site to meet some English speakers who want to learn Mandarin, and then do a language exchange. _____________________________________ Since I don't know how much English you know, I'll write a much more simple version of what I just said in case you were confused. Use flashcards for learning new words. When you memorize enough words (1000 or more), find English speakers on italki. Teach them Mandarin, and they will teach you English.

Definitely through usage. If you've learned a few new words, try to use them during the day. Also, there are quite a lot of patterns you will come across as you expand your vocabulary. Those patterns will definitely help improve your efficiency when memorizing words. For example, try to remember word endings (tion/sion/cate/late and etc).You will be able to apply those to learning quickly.