Knowing the meaning of expressions is different to being
able to apply them automatically. Vocabulary is not useful
until it's at the tip of your tongue.

So,
Memorize key words – since you
will not have time to look for them
when needed.
Knowing the meaning of words is
not enough. They aren't useful until
you've been through the whole
learning cycle. This implies that you
have to understand the word, know
how to use it, memorize it and be
able to recall it when needed.
Try to revise vocabulary a week
after you've learned it and check if
you remember it one month later.