I've been to London before so I know the ropes.

我去过伦敦，所以我了解伦敦的状况。

The moment she got to know the ropes, there was no stopping her.

一旦她懂了行，她就一往无前了。

I've been to the United States before so I know the ropes.

我去过美国，所以我熟悉那里的风土人情。

After two years in college, I think I finally know the ropes.

进了大学二年了，我想我终于懂得诀窍了。

I've been to China before, so I know the ropes. Can I help you?

我以前去过中国，所以我了解中国的情况，我能帮你什么忙吗？