Practice makes perfect goes the old proverb. Nothing can substitute good preparation.
I remember in high school before any event we had to go through vigorous rehearsals to make sure everything is right. In my time I've also participated in a number of drama productions and know how important preparation is. every time you see a good performance on stage, you best believe a lot of work went into that. Of course we all know about exams and how we must prepare for them.
Generally for whatever we do, good preparation makes a world of difference, let the day not find you unprepared. Remember the story of the virgins in Matthew 25? the wise ones were ready when the bridegroom came.
Don't get caught out, be ready!