Translation from memory. Translate a poem that you remember fairly well, but not word for word. Don't look at the actual text, or think too much about specific words Here's one from Luis Cernuda:

"I never thought I'd ever again evoke the
memory of your ancient name. But one
of that tribe, supposedly a poet (how
far our country has fallen!) and, so they say,
a critic of our 'Contemporary Spanish
Literature" has called you "my dead prince."
And I have to wonder: what the hell did you
ever do for him to make him call you his "prince"?

Academic vulgarity? A more deranged vulgarity
is evident in his lines. But I think there's something else at work.
It was not enough for them to have killed you.

Now assassination gives way to idiocy."

I'm sure I've left out some lines or altered the text in a way easily corrrected. I think the excercise is useful, all the same.