Ich vergass, me olvidé, 我忘記了, I forgot

A day or two ago I wrote about my interest in languages (and it's relevance for my faith). When I first posted it, I forgot to mention that in addition to making my way through German, Spanish, Chinese and biblical Greek, I will also begin studying Arabic on 12 March. It dawned on me I could use some learning advice from any linguophile readers.

So, any good tips for 1) perfecting German, 2) improving Spanish and Chinese (hopefully to a very high level), reading biblical Greek and/or 4) getting a good basic grasp of Arabic? (Maybe I should just be a philologist, comparative literarian, or interpreter.)

Now's your chance to shine, language lovers, I'm all tongues ears!