in my opinion, good english means 'speaking without thingking', thinking about how to say something in english

Each of us has our own English. I hear many people speak with accent and there is nothing wrong with it. Some accents are very nice. Just if a one feels satisfied with how he or she speaks or understands others..I think then he or she has a good English.

In my opinion, to be good in english you've to practice on how to speake , learn idioms and expressions as the native speakers

If you can understanding any words from british accent and you can speak as them, that's enough

I thing grammar is more important to learned, but i've ever heard that "memorize every words by someone is more important than memorize sentence structure" and i've been learning grammar, more 5 years and i get nothing.