For those of you who are going to face the Cambridge First Certificate or the Advanced one this coming Saturday, here are some expressions we would like to say to you:
This expression is used for telling someone that you wish him/her success.
Break a leg
This expression is used for wishing someone good luck.
(The) best of luck
This is used for wishing someone good luck in something he/she is trying to do.
We wish you much success and of course all the best of luck!