500 words a week is simply far too much. You're not going to be able to retain most of them in such a short period of time, which basically makes it a waste. Like Dmitry said, consume English media and talk to natives; you'll learn the most common words naturally, and then you'll branch out from there to pick up useful words and phrases until you've got a strong enough vocabulary to understand 80-90% of an average sentence. From there, new English words will just fall into place, in the same way they fall into place when learning new Arabic words.

I don't advice you learn just words. If you dont' use all these words routinely, you gonna forget it even if you are able  to learn all of them. The best way of studying is practise, watch movies, listen songs and talk to native speakers :)